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Survival of Food Crops 
and Livestock in the Event 
of Nuclear War 



Proceedings of a symposium held at 
Brookhaven National Laboratory 
Upton, Long Island, New York 
September 15-18, 1970 

Sponsored by 

Office of Civil Defense 

U. S. Atomic Energy Commission 

U. S. Department of Agriculture 



Editors 

David W. Bensen 
Office of Civil Defense 
Arnold H. Sparrow 

Brookhaven National Laboratory 



US DEPARTMENT- H ; .CULTURE 
NATIONAL AGRiCUL URAL LIBRARY 

OCT 28 1996 

^'CATALOGING PREP. ; > 



December 1971 



U.S. ATOMIC ENERGY COMMISSION Office of Information Services 



AVAIL AS CONF-700909 FOR $26,75 

FROM 

NATIONAL TECHNICAL INFORMATION SV 

U*S* DEPARTMENT OF COMMERCE 

SPRINGFIELD MA 22161 



Library of Congress Catalog Card Number: 77-170334 

Printed in the United States of America 

USAEC Technical Information Center, Oak Ridge, Tennessee 

December 1971 



FOREWORD 



Since its inception, the Brookhaven National Laboratory has had 
a deep and active interest in the effects of radiation, including 
radiation from fallout. As examples of this interest, we can list the 
East River Project, carried out in large part by the laboratory many 
years ago; the initial and continuing care of the Marshallese who 
were accidentally exposed to large doses of fallout radiation in 1954; 
and the extensive studies at Brookhaven on the effects of radiation 
on animals and plants. 

The particular interest at this symposium is radiation effects 
resulting from high-dose exposure, rather than the effects of 
low-level exposure (i.e., doses and dose rates commensurate with the 
radiation-exposure guides for radiation workers and for the public). 
These studies, of course, have a strong pragmatic component, in that 
the objective is to develop the ability to predict the potential effects 
of large doses of radiation on man directly and indirectly via possible 
detrimental effects on animals and food crops and via isotopes in the 
food chain. We must be able to evaluate the relative importance of 
these and other factors in the overall damage situation following 
nuclear warfare. 

However, I do not need to remind you that studies on the effects 
of radiation have led and will continue to lead to very basic findings, 
the importance of which transcends pragmatic considerations. For 
instance, Arnold Sparrow's excellent work on the relation of the 
chromosome volume to radiation sensitivity has told us a great deal 
about the sensitive unit within the cell. The entire concept of repair 
at a molecular or biochemical level grew out of radiation studies. 
Whole new areas of scientific endeavor owe their effective origin to 
radiation studies. Cell and tissue kinetics, now a very large field 
involving many hundreds of investigators, grew from the need to 
understand these processes both in the context of the effects of 
radiation of the entire animal and plant and of radiotherapy. The 



FOREWORD 

field of tissue transplant, now progressing at an accelerated pace, 
owes its origin to early attempts to modify radiation injury in the 
mammal by means of bone-marrow transplants. Immunology also 
received enormous impetus from findings derived from studies of 
impaired immunological response following large doses of radiation. 
These examples remind us that, while many of the goals of this 
symposium are pragmatic, these investigators are indeed dealing with 
very basic problems in sciences. 



V. P. Bond 

Associate Director 

Brookhaven National Laboratory 



PREFACE 



Results of ongoing research and study reported in these symposium 
proceedings should significantly improve the ability to forecast and 
assess the postattack availability and safety of food should a nuclear 
attack on this country occur. This improvement could not have 
occurred, of course, without an accompanying expansion in knowl- 
edge of the basic scientific phenomena involved. 

A number of the problems that would confront the nation 
following nuclear attack were identified and discussed in the 
proceedings of a symposium on Postattack Recovery from Nuclear 
War held at Fort Monroe, Virginia, in November 1967. 

The consensus of the symposium was that, after such an attack, 
crippling problems of food, health, ecology, and long-term effects on 
man were unlikely. Major areas of greatest doubt and less optimism 
were those of postattack management (including both government 
and private sectors of the economy) and of motivations, incentives, 
and behavior of the population at all levels. 

Since the Fort Monroe meeting, significant new information on 
the food problem has been developed. In particular, sufficient new 
research data on the effects of fallout radiation — both beta and 
gamma — on food crops and livestock have accumulated to warrant a 
symposium to review and consolidate these data and to make them 
available for planning purposes. 

The conclusion of the earlier symposium that crippling problems 
of food appear unlikely remains valid when applied to the total 
resources that should be available to the nation. However, it is 
certain that there would be serious local shortages and that damage 
to individual crops and herds would be extensive. 

This symposium serves two other important purposes: (1) It 
provides an improved communication link between the users of 
research information and the scientists who produce it. (2) Perhaps 
of equal significance, it demonstrates a mutuality of interests among 



PREFACE 



the three sponsoring federal agencies, the Office of Civil Defense, the 
Atomic Energy Commission, and the Department of Agriculture. 

Although this symposium indicates that the broad dimensions of 
the postattack food-supply problems are generally understood, some 
uncertainties still exist. Through discussions and working group 
sessions, the types of additional research and study needed to clarify 
this important aspect of national survival were identified. 

To this end an Interagency Technical Steering Committee 
represented by the Office of Civil Defense, the Atomic Energy 
Commission, and the Department of Agriculture has been created 
for the purpose of coordinating and guiding research in which a 
mutuality of interest exists. 



John E. Davis 

Director of Civil Defense 



VI 



CONTENTS 



Session I: The Hazard — Properties of Fallout 

Introductory Remarks 1 

Jack C. Greene 

Physical, Chemical, and Radiological Properties 

of Fallout 9 

./. //. Norman and P. Wincbell 

Beta-Radiation Doses from Fallout Particles 

Deposited on the Skin 31 

S. Z. Mikhail 

Measurement and Computational Techniques 

in Beta Dosimetry 51 

James Mackin, Stephen Brown, and William Lane 

Measurement of Beta Dose to Vegetation 

from Close-in Fallout 56 

A. D. Kantz 

The Importance of Tritium in the 

Civil-Defense Context 71 

J. R. Martin and J. J. Koranda 

Properties of Fallout Important to Agriculture 81 

Carl /•'. Miller 

Preparation and Use of Fallout Simulants 

in Biological Experiments 107 

William B. Lane 



VII 



CONTENTS 

Session II: Fallout-Radiation Effects on Livestock 

Fate of Fallout Ingested by Dairy Cows 115 

G. D. Potter, G. .If. Vattuone, and D. R. Mclntyre 

Fate of Fallout Ingested by 

Swine and Beagles 125 

Robert J. Cbertok and Suzanne Lake 

Radionuclide Body Burdens and Hazards 
from Ingestion of Foodstuffs Contaminated 

by Fallout 131 

Yook C. Ng and Howard A. Tewes 

Retention of Simulated Fallout by 

Sheep and Cattle 173 

James E. Johnson and Arvin I. Lovaas 

Simulated-Fallout-Radiation Effects 

on Sheep 178 

L. B. Sasser, Vf. C. Bell, and J. L. West 

Simulated-Fallout-Radiation Effects 

on Livestock 193 

M. C. Bell, L. B. Sasser, and J. L. West 

Pathology of Gastrointestinal-Tract 

Beta-Radiation Injury 208 

J. L. West, .11. C. Bell, and L. B. Sasser 

Responses of Large Animals to Radiation Injury 224 

David C. L. Jones 

Criteria for Radiation Injury 234 

John S. Krebs 

Species Recovery from Radiation Injury 245 

J. F. Spalding and L. M. Holland 

Radioiodine Air Uptake in Dairy Cows 

After a Nuclear-Cratering Experiment 259 

Ronald E. Engel, Stuart C. Black, 

Victor W. Randecker, and Delbert S. Barth 

Problems in Postattack Livestock Salvage 269 

S. A. Griffin and G. R. Eisele 



VIM 



CONTENTS 

Session III: Fallout-Radiation Effects on Plants 

Exposure-Rate Effects on Soybean Plant 

Responses to Gamma Irradiation 277 

M. J. Constantin, D. D. Killion, and E, G. Siemer 

Effects of Acute Gamma Irradiation on 
Development and Yield of Parent Plants and 

Performance of Their Offspring 287 

E. G. Sienier, M. J. Constantin, and D. D. Killion 

Effects of Exposure Time and Rate on the 

Survival and Yield of Lettuce, 

Barley, and Wheat 306 

P. J. Bottino and A. II. Sparrow 

Dose-Fractionation Studies and Radiation-Induced 

Protection Phenomena in African Violet 325 

C. Broertjes 

Summary of Research on Fallout Effects on 

Crop Plants in the Federal Republic of German)- 343 

Hellmut Glubrecbt 

Radiation Doses to Vegetation from Close-in 

Fallout at Project Schooner 352 

W. A. Rhoads, II. I. Ragsdale, R. B. Piatt, and E. M. Romney 

Survival and Yield of Crop Plants 

Following Beta Irradiation 370 

Robert l\. Schuk 

Field Studies of Fallout Retention by Plants 396 

John I'. Witberspoon 

Retention of Near-In Fallout by Crops 405 

A. I. Lovaas and J. /.. Johnson 



Session IV: Effects of Fallout Radiation on 

Agricultural and Natural Communities 

Prediction of Species Radiosensitivity 419 

Harvey L. Cromroy, Richard Levy, 
Alberto B. Brace, and Leonard J. Goldman 



IX 



CONTENTS 

Insect-Induced Agroecological Imbalances as an 

Analog to Fallout Effects 434 

Vernon M. Stern 

Ecological Effects of Acute Beta Irradiation 
from Simulated-Fallout Particles on a 

Natural Plant Community 454 

Peter G. Murphy and J. Frank McCormick 

Effect of Nuclear War on the Structure and 
Function of Natural Communities: An Appraisal 

Based on Experiments with Gamma Radiation 482 

G. M. Woodwell and B. R. Holt 

Prediction of Radionuclide Contamination of 

Grass from Fallout-Particle Retention and Behavior 492 

Roger C. Dahlman 

Responses of Some Grassland Arthropods to 

Ionizing Radiation 509 

Clarence E. Styron and Gladys J. Dodson 

Survival of Crickets, Acheta domesticus (L.), as 

Affected by Variations in Gamma Dose Rate 521 

R. I. Van Hook, Jr. 

Effects of Beta— Gamma Radiation of Earthworms 

Under Simulated-Fallout Conditions 527 

David E. Reicble, John P. Wither spoon, 

Myron J. Mitchell, and Clarence E. Styron 

Cesium-137 Accumulation, Dosimetry, and Radiation 

Effects in Cotton Rats ' 5 35 

D. DiGregorio, P. B. Dunaway, 

J. D. Story, and J. T. Kitchings III 

Session V: Considerations in Agricultural Defense Planning 



The Significance of Long-Lived Nuclides 

After a Nuclear War 

R. Scott Russell, B. O. Bartlett, and R. S. Bruce 



548 



Control of Fallout Contamination in the 

Postattack Diet 

J. C, Thompson, Jr., R. A. Wentworth, and C. L. Comar 



566 



CONTENTS 

Sensitivity Analysis of Agricultural Damage Assessment ... 595 
Stephen L. Brown 

Application of Damage- Assessment Data in 

U. S. Agricultural Defense Planning 608 

Bruce M. Easton 

United Kingdom Considerations in Agricultural 

Defense Planning 616 

W. T. L. Neal 

Appendix A: Reports of Committee Working Groups 

Committee 1 : Vulnerability of Livestock to 

Fallout Beta and Gamma Irradiation 627 

Committee 2: Vulnerability of Crops to 

Fallout Beta Irradiation 630 

Committee 3 : Vulnerability of Crops to 

Fallout Gamma Irradiation 63 3 

Committee 4: Beta Dosimetry: Calculational 

Techniques and Measurements 637 

Committee 5: Fallout Radiation Fields 639 

Committee 6: Radioecological Effects of 

Fallout Radiation 643 

Committee 7: Use and Requirements for Research 

Data in Agricultural Defense Planning .... 645 

Appendix B: Radiation Effects on Farm Animals and Crops 

Vulnerability of Livestock to Fallout 

Gamma Radiation 648 

Edwin T. Still and Norbert P. Page 

Radiation Effects on Farm Animals: A Review 656 

M. C. Bell 

The Effects of External Gamma Radiation 

from Radioactive Fallout on Plants, with 

Special Reference to Crop Production 670 

A. H. Sparrow, Susan S. Scbwemmer, 

and P. J. Bottino 

List of Attendees 712 

Author Index 719 

Subject Index 721 



XI 



INTRODUCTORY REMARKS 



JACKC. GREENE 

Office of Civil Defense, Washington, D. C. 



May I extend a warm welcome to you all. I am highly gratified at the extent of 
interest in the subject matter of this symposium, as evidenced by our fine roster 
of speakers and by the size and diversity of the audience. John E. Davis, 
National Director of Civil Defense, asked me especially to note his interest in the 
proceedings of the symposium and his concern about the problems to be 
discussed. He wished us a very successful meeting. 

As perhaps most of you know, this is the fourth in the series of conferences 
on the general subject of survivability of food crops and livestock in the event of 
a nuclear attack. The first, which was primarily an organizing and planning 
session, was held at Estes Park, Colo., in June 1967. The second was in Oak 
Ridge, Tenn., in May 1968. By the time of the third, which was held in June of 
last year in Fort Collins, Colo., a sufficient body of research data highly relevant 
to the civil-defense question had become available and needed to be reported 
and recorded in the literature. That was when the idea for the Brookhaven 
Symposium germinated, and the decision was made that for the first time we 
would ask for manuscripts of the papers to be presented. We are highly pleased 
that the Atomic Energy Commission has agreed to publish these papers as a 
volume in their Symposium Series. 

The research fraternity represented here is relatively quite small. If we were 
to give proper credit to all those who have contributed to the recent very rapid 
expansion of knowledge in this field, we would have to list, as a minimum, all 
the speakers for the symposium. Let me, however, acknowledge only a few. 
Arnold Sparrow, our host and cochairman of the conference, has pioneered in 
studies of plant radiosensitivity. We should note also the contributions of 
Nathan Hall, Vernon Cole, and Carl Bell, whose foresight and painstaking 
preparatory work lead to the definition of the Office of Civil Defense's research 
program in this area. And, finally, on behalf of the Office of Civil Defense, I 



2 GREENE 

wish to acknowledge formally the fine spirit of cooperation displayed by our 
cosponsors of the symposium, the Department of Agriculture and the Atomic 
Energy Commission. 

Now I shall take a few minutes to, in effect, step back from the focus on 
food survivability and attempt to provide a perspective on how food fits into the 
overall problem of survival and recovery from nuclear attack. Obviously food is a 
necessary consideration for survival, but food alone is not sufficient for survival. 
My purpose here is to point out to you some of the other constituents of 
sufficiency. To do this I shall employ a flow diagram model of U. S. society 
during and after a nuclear attack (Fig. 1). The descriptive material in the 
following paragraphs about the flow-diagram transfer coefficients is based on a 
very large number of research studies conducted over the past several years by 
personnel and contractors of the Office of Civil Defense and other organiza- 
tions.* 

If P is the size cf the U. S. population immediately prior to a nuclear war, 
then what happens to P as a result of the war can be examined in terms of the 
flow diagram shown in Fig. 1. 

If the initial flow input is of magnitude P and each of the attack effects is 
represented by an impediment, or barrier, to flow, then the value of the transfer 
coefficient represents the fraction of population that successfully passes the 
particular barrier to which a given coefficient applies. (It may be useful to think 
of each barrier as a sort of semipermeable membrane.) 

The fraction of the preattack population which survives all the attack effects 
is the product of the transfer coefficients a'b'c'd'e'f'g'h'i. Clearly 
the objective of a civil-defense system (or any other military offense or defense 
system) is to make this product as large as possible. It is equally clear that if any 
single transfer coefficient is critically small, there is no point in attempting to 
raise the others until the critical one is also raised. 

Each of these transfer coefficients will now be discussed in turn, both in 
terms of probable range of values and in terms of action needed either to lessen 
the uncertainties about the coefficients or to increase their values. 

Direct Weapons Effects. The transfer coefficient for direct weapon effects, a, 
represents the fraction of the preattack U. S. population surviving the blast and 
initial thermal and nuclear radiation. For today's civil defense, a probably would 
be in the range of 0.5 to 0.8, depending on the type and weight of attack. 
Employment of antiballistic missiles, blast shelters, or preattack evacuation 
increases a. 

Fallout, The transfer coefficient for lethal fallout effects, b, represents the 
fraction of the population surviving the direct effects (a) and also surviving the 



* Those wishing to pursue a particular point or to obtain specific references may do so 
by communicating with me at the following address: Postattack Research Division, Office of 
Civil Defense, The Pentagon, 1E542, Washington, D. C. 20310; Phone: Area 202, 695-9613. 



INTRODUCTORY REMARKS 3 

hazard of lethal fallout-radiation doses. Typical results of hypothetical attacks 
indicate that b would be in the range of 0.4 to 0.8. The value of b can be 
increased cheaply, at least on the margin; i.e., expenditures to save lives with a 
fallout shelter program are highly cost effective, as are expenditures to educate 
the public on the nature of the fallout threat and means of protecting against it. 



OH 

m > 
nz 

Tl CO 
GS 

m 3D 



' 


FLOW INPUT 

WWHH 


O 

-o 

■or 

^> 

-H 

O 

z 


CO -I 

Hm 
> 

-\ 
H 
> 

O M 
7^ 


Q) 


Direct blast and thermal effects 


1 to 2 days 




HHH 


CD 






cr 


Lethal fallout-radiation effects 


3 to 4 days 




HU 


CD 

cr 






o 


Trapped or not medically treated 


2 to 7 days 




WW 


CD 

& 

o 






Q. 


Inadequate life support 


5 to 50 days 




HH 


Q. 






CD 


Epidemics and diseases 


2 weeks 
to 1 year 




(a..e)P 






- 


Economic chaos 


1 to 2 years 




(a..f)P 






CO 


Late radiation effects 


5 to 20 years 




III! 








D" 


Ecological catastrophe 


1 to 50 yea 




WW 


CD 

-D 






- 


Genetic damage 


2 to several 
generations 




WW 

OUTPUT 


CD 









Fig. 1 Flow-diagram model of U. S. society during and after nuclear attack. 



4 GREENE 

For just these reasons the emphasis of the current civil-defense program is on 
fallout protection. 

At this point the flow diagram may be used to illustrate the importance of 
viewing civil defense as a system. A certain tactic intended to raise b may appear 
highly attractive if a narrow perspective is applied (suboptimization). But if this 
tactic at the same time reduces some other transfer coefficient, say a, so that the 
product ab becomes less than it was before, the tactic obviously is not desirable. 
For example, a policy of sending people to the upper stories of high-rise 
buildings to increase fallout protection in target areas may decrease b, but the 
accompanying increase in a (deaths due to initial weapons effects) may result in 
a net decrease in the number of people surviving both effects. Table 1 indicates 
how a and b might vary as a function of the weight of attack. 

Table 1 

TRANSFER COEFFICIENTS a AND b AND THEIR PRODUCT 
FOR VARIOUS WEIGHTS OF ATTACK* 



Transfer 


1000 


3000 


5000 


7000 


9000 


coefficient 


Mtt 


Mt 


Mt 


Mt 


Mt 


a 


0.78 


0.64 


0.57 


0.54 


0.49 


b 


0.81 


0.70 


0.58 


0.48 


0.39 


a * b 


0.63 


0.45 


0.33 


0.26 


0.19 



*Data are based on a composite of damage-assessment studies by the 
Department of Defense. The attacks were assumed to be against 
military— urban— industrial targets, and people were assumed to use the best 
protection available in the normal place of residence. 

tUnits of attack weight are in megatons equivalent of TNT. 



Rescue and Medical Care, The transfer coefficient c is attributable to the 
effectiveness of emergency operations services, such as rescue and medical teams 
and represents the fraction of the population surviving blast, thermal, and fallout 
effects, not already foredoomed to die, which could and would be saved by 
rescue and emergency medical care. Contrary to much prevalent intuition, c 
probably is a fraction near 1. The reason for this is not that rescue and medical 
care are expected to be highly effective, but that the percentage of people that 
could be rescued in time or could be saved by medical care is very small. 
Therefore expenditures to increase c do not appear to very cost effective. (The 
value for c is probably greater than 0.95.) 

Life-Support Requirements. The transfer coefficient d represents survival during 
the very early postattack period when people in shelters or other isolated 
locations could be running out of food or water or the shelters (because of 
inadequate ventilation) might become intolerable. The value of d depends on 



INTRODUCTORY REMARKS 5 

how rapidly food-, water-, and power-distribution systems can be reestablished 
and how rapidly an effective emergency management system evolves. In some 
localities and under some conditions, the problems could be severe. Very hot or 
very cold weather, radiological constraints, and disrupted transportation and 
communications systems could have a serious impact. This area requires more 
study and the development of individual plans tailored to the needs of individual 
localities and situations. On a national average, however, d is not likely to fall 
much below 1.0. 

Epidemics and Diseases. The transfer coefficient for epidemics and diseases is e. 
Postattack health problems could be exacerbated because of disrupted water and 
sewerage systems, malnutrition, and radiation exposures. The range of e might 
be wide, but, with reasonable precautions and attention, it probably could be 
kept high. The national average value for e should be above 0.95. Additional 
study and development of contingency plans for specific health problems that 
might occur are needed and are being undertaken. 

The Economy. The transfer coefficient accounting for the requirement that the 
economy become functional and produce the commodities essential to sustain 
the attack survivors before surviving inventories are used up is f. In this respect it 
is particularly fortuitous that the U. S. agricultural industry is highly efficient. 
About 6% of the U. S. population produces not only enough food to feed 
America but also vast quantities for export. 

Numerous studies show that the physical wherewithal (transportation, 
fertilizer and petroleum products, essential industry, etc.) to continue to provide 
food to sustain the survivors of a nuclear attack would also survive. This 
damaged economy could provide for an adequate diet and for the other items 
essential to survival without undue strain, and a surplus of labor, capital, and raw 
materials would be left with which to rebuild the economy. It is not enough, 
however, to say that the physical capacity to sustain survivors would exist. One 
has only to recall that there was no physical incapacity of the nation's ability to 
produce in the late 1920's and early 1930's during the worst depression of U. S. 
history. The machine was in good shape-, the problem was that management did 
not know how to operate it. To expect efficient or even adequate operation of 
an economy damaged by a massive nuclear attack, with the attendant social and 
psychological trauma, may be highly optimistic. 

If there is an Achilles' heel in the postattack recovery system, it probably lies 
in f, the transfer coefficient relating to economic chaos. But this Achilles' heel, if 
it exists, is not inherent; it would result from inadequate planning and 
preparations for management rather than from limitations of the physical 
capacity to produce. 

Late Radiation Effects. The transfer coefficient g accounts for the people who 
would die from bone cancer, leukemia, thyroid damage, and other radiation- 
induced effects. Although the impact on the survivors might well be detectable 



6 GREENE 

(and might have a more important psychological than physiological impact), 
these late radiation effects pose little threat to the society's survival. The value 
of g probably is a number greater than 0.99. The research in this area is done 
largely under AEC and U. S. Public Health Service sponsorship. Charles L. 
Dunham (former Director of the AEC Division of Biology and Medicine and 
currently the Chairman of the Division of Medical Sciences, Academy of 
Sciences) recently summarized the long-term effects with the following 
statement: "20,000 additional cases per year of leukemia during the first 15 to 
20 years postattack followed by an equal number of cases of miscellaneous 
cancers, added to the normal incidence in the next 30 to 50 years, would 
constitute the upper limiting case. They would be an unimportant social, 
economic, and psychological burden on the surviving population." (The Dunham 
statement was in reference to specific hypothetical attacks — one, CIVLOG, was 
a 45 5-weapon 2000-Mt attack; the other, UNCLEX, was an 800-weapon 
3 500-Mt attack. Current status of civil defense was assumed.) 

The yearly rate appearing today for the 200-million U. S. population is 
about 20,000 new cases of leukemia. There are about 15,000 deaths per year 
due to this cause. 

The Ecology. The transfer coefficient h accounts for the damage to the ecology 
which could occur from the nuclear attack. Probable ecological consequences of 
nuclear war are still uncertain. Extensive research programs are underway, and 
progress is being made. The most comprehensive program, at least in the Western 
World, is that of the Radioecology Section of the Oak Ridge National 
Laboratory — research partially supported by OCD over the last several years. 

The "doom and gloom" predictions prevalent in the late 1950's and early 
1960's are not supported by this research. The summary report of Project 
Harbor, a 1963 study of civil defense by a committee of the National Academy 
of Sciences under the leadership of Eugene Wigner, contains this statement: 
"Large-scale primary fires, totally destructive insect plagues, and ecological 
imbalances that would make normal life impossible are not to be expected." In 
the 1969 study (again under the leadership of Dr. Wigner) intended to update 
the Project Harbor work, is the following statement: "A reasonable conclusion, 
therefore, is that the long-term ecological effects would not be severe enough to 
prohibit or seriously delay recovery." 

Some perspective as to the possible ecological effects of a nuclear attack can 
be gained by considering that man is now, in peacetime, doing just about 
everything he can do to upset the ecological balances. The ultimate results on 
the ecology of water and air pollution and of widespread application of 
herbicides and insecticides are beyond our knowledge to predict; but, whether or 
not there is a nuclear war, these problems have to be faced and solved. At this 
point in the flow diagram, it is no longer feasible to ascribe a numerical value to 
the transfer coefficient. By the time these ecological consequences would 
manifest themselves, limiting the growth of population might have again become 



INTRODUCTORY REMARKS 7 

a socially desirable goal. But to think that the ecological damage of nuclear war 
would be so severe as to limit flow in the concept of the diagram is just not 
justified. (Though verging on the macabre, it should be pointed out that a 
nuclear war could alleviate some of the factors leading to today's ecological 
disturbances that are due to current high-population concentrations and heavy 
industrial production.) 

Genetic Effects. The transfer coefficient for genetic damage, i, is included 
primarily for completeness. Genetic effects, like late radiation and ecological 
effects, are widely misunderstood, and consequently feared, and probably have 
aroused more emotional heat then the others. Although g, h, and i could be 
important, there is little question that they represent minor consequences 
compared with others. 

The genetic effects of radiation exposure have received a great deal of 
study — with animals in the laboratory and with humans in follow-up studies of 
people given radiation for therapeutic and diagnostic purposes, people involved 
in accidents, and the survivors of Hiroshima and Nagasaki. The Atomic Bomb 
Casualty Commission, a joint U. S.— Japanese study, has had an extensive 
program underway in Japan since the early days following World War II. 

Dr. Dunham, in the same summary referred to previously, said, "The genetic 
effects would be lost, as at Hiroshima and Nagasaki, in all the other 'background 
noise'." 

The concepts that people harbor about late radiation, ecological, and genetic 
effects probably are far more severely distorted than those concepts about any 
of the other potential attack effects. To illustrate, in May 1970, The New 
Yorker magazine's lead article contained the following statement: "Since the 
development of nuclear weapons, everyone has known that an international 
crisis could lead to the extinction of the human species." Other examples just as 
dramatic can be found in Robert Kennedy's book on the Cuban crisis. The 
following quote is typical: "Each one of us was being asked to make a 
recommendation which would affect the future of all mankind, a recommenda- 
tion which, if wrong and if accepted, could mean the destruction of the human 
race. " (Italics in both references are used for emphasis.) 

I cannot prove by this flow-diagram model or by any other analytical device 
or line of reasoning that this country could survive and recover from a nuclear 
attack, any more than I can prove that we will satisfactorily solve our pollution 
or population-growth problems or work out a more acceptable rapprochement 
with our young. On the other hand, when people make dogmatic statements to 
me claiming that we could not survive and recover from a nuclear attack, I defy 
them to identify in accordance with this or with any other model the barrier or 
barriers that would be insuperable. 

In any case, I am firmly convinced that our chances of survival and recovery 
from a nuclear catastrophe, should it occur, will be much higher, the progress 



8 GREENE 

much faster, and the trauma less severe if we have studied and understand the 
potential problems and have figured out the best ways of handling them. 

An absolute requisite at any stage of the recovery process is an adequate 
supply of food that is nutritionally sufficient and radiologically acceptable. The 
work that is being reported here constitutes, I believe, a giant step toward 
understanding the physical and physiological components of this food problem. 
More work is needed, especially work to improve the plans and procedures for 
allocation and distribution of food. If civil defense, like the army, "must travel 
on its stomach," the work you are doing will help assure that the wherewithal 
to travel is in plentiful supply. 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL 
PROPERTIES OF FALLOUT 



J. H. NORMAN and P. WINCHELL 

Gulf General Atomic Company, San Diego, California 



ABSTRACT 

The importance to a biological-damage model of physical chemistry associated with the 
sorption of fission products by fallout is suggested. Calculated sorption behavior for Small 
Boy fallout of several nuclide chains is demonstrated according to a condensed-state 
diffusion-limited sorption model. An experiment on glassy Johnie Boy fallout revealed a 
diffusion-controlled profile of Cs in partial support of the calculated model. 

To describe the biological activity of the various fission-product nuclides, we must 
understand the leaching properties of radionuclides in the fallout particles. As an initial 
report on our work in this field, we considered sorbed iodine transport in contact with 
(1) moist air and (2) solutions. Sodium and iodine leaching from several glasses was also 
studied. Leaching of fission products from a CaO— AI2O3— SiC»2 glass a few days after recoil 
loading was studied. In these leaching studies the data were fitted to several models: 
surface-reaction-rate-limited, diffusion-limited, and desorption-limited processes. The ob- 
servation of the pertinence of several models suggests considerable complexity in a leaching 
model for fallout. 



The most important questions in characterizing fallout with respect to a 
biological-damage model are: 

1. How much fallout has been deposited in the region of concern? 

2. How much radioactivity as a function of time is associated with the 
fallout? 

3. What is the distribution of the radioactivity with respect to the fallout 
particles? 

4. What is the physical, chemical, and radiological behavior of the particles 
with respect to the environment? 

Tolerance levels for various radionuclide exposures must be established, of 
course. Nevertheless, the essential doses and dose rates resulting from an 



10 NORMAN AND WINCHELL 

exposure to fallout are intimately connected with the description of the fallout. 
Therefore our premise is that knowledge of fallout properties is necessary for 
radiological-damage estimates, and thus a damage model must incorporate a 
fallout model as a base. 

During the last two decades, there has been a considerable effort to 
formulate a physical— chemical fallout-formation model. Fractionation of 
volatile fission products was noted early by Freiling. Models have been 
constructed, for instance, by Freiling, 2 Miller, 3 and Korts and Norman 4 to 
simulate fractionation. Considerable effort has been made to define the 
phenomena involved in fallout formation. Recently Freiling presented a good 
description of nonturbulent, nonagglomerating fallout formation in which 
fission-product sorption is described as controlled by one or more of three 
processes: gas-phase diffusion, condensed-phase diffusion, and surface condensa- 
tion. He presented a basic method for determining the importance of each of 
these processes to fallout formation. This method involves evaluating the basic 
chemical and physical parameters associated with each of these phenomena. 
Freiling lists these parameters as follows: 

1. Particle radii and distributions thereof. 

2. Vapor-phase diffusivities. 

3. Condensed-phase diffusivities. 

4. Henry's law constants (distribution coefficients). 

5. Condensation coefficients. 

6. Mean molecular speed of the gas-phase species. 

Information is available for most of these quantities for evaluating fallout 
formation. Particle-size distributions have been discussed many times. ' Heft's 
bimodal particles certainly should be considered. Vapor-phase diffusivities and 
mean molecular speeds can be readily derived from knowledge of the gaseous 
species and the pressures and temperatures encountered during fallout forma- 
tion. Norman 9 presented an estimate of Henry's law constants for silicates, and 
information on silicate diffusivities was presented by Winchell and Norman. 
Condensation-coefficient studies were performed by Adams, Quan, and Balk- 
well 1 1 and by Bloore et al. 1 2 Russell 1 3 also contributed to an understanding of 
several of these phenomena. 

Although the phenomenological studies have shown considerable promise, 
much less has been accomplished in terms of establishing a model incorporating 
the six parameters. Miller 3 provided the first physical— chemical model, which 
employed a step response in condensed-state diffusivity at a soil melting 
temperature, surface equilibrium, and Raoult's law constants (i.e., fission 
products were assumed to condense in silicates according to ideal-solution law 
until particles froze, and thereafter they were assumed to surface deposit). Korts 
and Norman 4 constructed a more general model in which a set of Henry's law 
constants 9 was employed along with silicate-diffusion constants to make 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 11 

approximate dynamic calculations of condensed-state profiles assuming that the 
gas phase was in equilibrium with the surfaces of the fallout particles. 

These models are very complex. An interdecaying population of fission 
products must be imposed on the kinetics of sorption. The set of differential 
equations to describe fully the decaying population and sorption by the three 
listed processes is extensive, and good, approximate solutions are difficult to 
achieve. 

The problem of obtaining a complete physical— chemical model, then, is 
discouraging to those looking for a quick answer. Some empirical models have 
been developed [e.g., the U. S. Naval Radiological Defense Laboratory 
(USNRDL) RAD model 2 ] which have proved quite useful, but they do not 
describe well some properties important to biological activity. 

At this point we will consider further the Korts— Norman model as a possible 
limiting physical— chemical description of fallout. Model features that should be 
important in fallout are the predicted fractionation, the nature of fission- 
product-penetration profiles, and the activity division according to particle size. 
These features can be calculated for a field of altered and unaltered fallout 
according to Heft's suggestions. 8 Fractionation affects the quantity and type of 
fission products encountered in a given region of a fallout pattern since 
sedimentation rates are particle-size dependent. Profiles affect the beta-dose 
rates from particles, as discussed by Mikhail, 14 and also the biological 
availability. The model output, together with a leaching description of the 
matrix, determines the mobility of fission products. The character of the fallout 
itself establishes the sorptive and leaching properties. Altered (from molten 
droplets to glassy spheres) and unaltered debris exhibit considerably different 
fission-product profiles. Late or peripheral entry of debris into the cloud is 
important, as are sorptive properties and leaching properties of the debris. 

The basic question is: What is necessary to provide a better physical- 
chemical description of fallout for use in a biological model? Our answer is 
twofold: (1) Establish fission-product profiles in fallout particles, and (2) estab- 
lish the degree of corrosion of and migration in fallout particles under 
appropriate conditions. The remainder of this paper bears on these two points. 



DESCRIPTION OF FALLOUT ACCORDING TO THE CONDENSED-STATE 
DIFFUSION-CONTROLLED FISSION-PRODUCT SORPTION MODEL 

The condensed-state diffusion model for fission-product absorption assumes 
(1) that the rate of fission-product sorption during the critical time— temperature 
regime is controlled by diffusion of surface-absorbed fission products into the 
bulk of fallout particles, (2) that the surface of a particle is in equilibrium with 
the neighboring gas, and (3) that the pressures of the gaseous fission products are 
locally constant (i.e., that gas-phase diffusion is fast enough that local 
fission-product pressure gradients are negligible). Descriptions of the calcula- 



12 



NORMAN AND WINCHELL 



10 22 



TIME, sec 
2 4 6 8 



10 21 - 



10 



20 _ 



z 10 19 - 



z 
o 

CJ 

LU 
CO 

< 

x 10 1f 

Q_ 

CO 
< 



10 17 



10 1 



10 1 



10 



Tc(9.0) 




CM CM *- «- 

TEMPERATURE, 



Fig. 1 Calculated gas-phase concentrations in 106 chain for Small Boy 
(ruthenium precursors and half-lives in seconds listed). 



tional methods and some parameter scaling for this model were presented by 
Korts and Norman. A short description of the model was given by Norman et 
al., and a parametric study including some simulated Small Boy calculations 
was presented by Norman et al. 1 6 In this report, some additional data from our 
Small Boy calculations are presented to demonstrate the properties of the model 
which are important to a biological-activity model. The Small Boy time- 
temperature history is approximated on the abscissas of Figs. 1 and 2, and the 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 13 



10 22 



10 1 



10 1 



10 lfa - 



TIME,sec 



10 



Xe(16) 




s Ce 
<\ I \ 


I 


I I I I I I 


| 


4000 
3600 
3200 
2900 


o 
o 
co 

CM 


o o o o o o 
o o o o o o 

^fr CM O 00 CD ^ 
CM CM CM <- .- .- 

TEMPERATURE, 


o 

o 

CM 

°K 



10 1 



Fig. 2 Calculated gas-phase concentrations in 140 chain for Small Boy 
(cesium precursors and half-lives in seconds listed). 



particle-size distribution is approximated on the abscissa of Fig. 3. Figure 1 
shows the calculated gas-phase content of elements in the 106 chain. This figure 
demonstrates the early condensation of Nb, which decayed about a factor of 
2 for the calculations shown although the niobium gas-phase content dropped 
five orders of magnitude when it cooled to 2600° K. The condensation of 
molybdenum at later times is demonstrated. Molybdenum does not condense 
appreciably until the fireball temperature drops to 2000° K, and then the 



14 



NORMAN AND WINCHELL 



molybdenum pressure drops sharply over the next few hundred degrees Kelvin. 
The moderate volatility of molybdenum is due to the species Mo0 3 (g). This 
figure further shows that neither technetium nor ruthenium condenses apprecia- 
bly all the way down to 800°K. The volatility of Ru0 3 (g), Ru0 4 (g), Tc0 3 (g) 
(Ref. 9), Tc 2 7 , or HTc0 4 [actually Tc0 3 (g) in this calculation] is thus 




10- 3 10- 2 

PARTICLE RADIUS, cm 



10- 1 



Fig. 3 Calculated 800 K concentrations for Small Boy. Each particle-size 
group contained 7.82 x 10 g of silicate-type fallout. 



reflected. However, most of the ruthenium and technetium should condense at 
lower temperatures. The point is that the diffusion coefficients at temperatures 
below 1200 to 1400 K are so low that condensing fission products are 
essentially surface loaded at these temperatures. Accordingly, niobium will 
volume load, molybdenum will exhibit a more surface-oriented profile, and 
ruthenium and technetium will surface load fallout particles. Note that, in a 
much larger detonation than Small Boy (1.5 kt), much of the 1 06 Nb and l 06 Mo 
could have decayed before the cloud cooled to condensing temperatures for 
these isotopes. If this were to happen, the 106 chain would be considerably 
more volatile since nearly 50% of the primary yield is in molybdenum and 
niobium. Also it is important to understand that a refractory element which has 
condensed at high temperature and which subsequently decays to a volatile 
element cannot efficiently vaporize at appreciably lower temperatures, because 
of condensed-state diffusion limitations. 

Another interesting chain, 140, is considered in Fig. 2. The gas-content 
curves show lanthanum coming down at high temperatures (volume loading). 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 15 

This is correct for the lanthanum existing in this time regime; however, since 
lanthanum is a daughter of barium and barium is a daughter of cesium, etc., the 
140 La observed experimentally in fallout displays the properties of its 
precursors, and the small initial lanthanum yield is masked. Barium behaves like 
a fairly refractory element and will essentially volume load. However, it is a 
daughter of less refractory elements, and thus the barium observed in fallout is 
mixed in character. A moderate amount volume loads, whereas the barium from 
cesium exhibits a profile intermediate between volume loading and surface 
loading. The barium contributed from xenon and iodine is largelv associated 
with the surface. The result of this is shown in Fig. 3, where the calculated 
average concentrations of lanthanum, barium, and cesium in the various-size 
fallout particles 9.8 sec after detonation are demonstrated. Lanthanum shows 
the same concentration for all size particles (volume loading), but barium 
exhibits a small change in concentration. For big particles the effect is a 
diffusion limitation of the original barium, and for small particles the increasing 
slope is caused by cesium's decaying to barium, a process that will later generally 
dominate the barium concentrations. The cesium values exhibit surface-loading 
characteristics. Pure surface loading in this model would be given by the average 
concentration's being inversely proportional to the particle radius; i.e., 
C = k[47rr /(47rr /3)] . Figure 4 shows the ratio of surface concentration to 
average concentration of all the isotopes in a chain for various chains for the 
particle ensemble at 800°K, along with the remaining gaseous fraction at 800 K. 
Where the concentration ratio is near unity and little material is left in the gas 
phase, the chains will volume load. The further this is from being the case, the 
more highly surface loaded the chain will be. This plot is in good relative 
agreement with the experimental data. In an earlier paper 1 6 a reasonable check 
with Small Boy data was demonstrated for the 89 chain. 

This model is capable of handling various inhomogeneities. A crystalline 
phase can be injected at some time when the cloud is lower in temperature than 
the melting point of the crystals. This would correspond to some of Heft's 8 
observations. We can segment the problem so that different properties could be 
assumed in different sections of the cloud. Detachment of particles and cloud 
can be handled easily. Mathematically, intraparticle turbulence and particle 
agglomeration are not permitted. The question then becomes: How realistic is 
this model? At least we can say that it is a limiting condition. Condensation rates 
would not normally be considered to exceed the rates used in this condensed- 
state diffusion model. Under certain conditions, e.g., when a great deal of 
condensation was taking place, gas-phase diffusion would be rate limiting. This 
could slow up condensation so that fission products would be more surface 
sorbed than predicted with this model. It could instead be true that a 
condensation step would be rate limiting. In this case the final result would again 
predict more surface sorption. We believe that, in the absence of a complete 
calculational model, our condensed-state diffusion model is a good place for 
biological models to begin. 



16 



NORMAN AND WINCHELL 



10 E 



10V 



LU O 



10 s 



10' 



10 - 



- 




I 


! 


! 


I 


I 


I 


I 

o 


I 
o 


- 


- 





















- 


- 


I 


9 


O 

i 


o 

I 


o 

I 


o 

I 


o 

I 


I 


I 


- 



1.0 r 
0.8 
0.6 
0.4 
0.2 




- 


I 


I 


I 


I 

o 


I 


I 


I 


I 
o 


I 


- 
















o 








- 


o 

I 


A 


O 
I 


I 


A 


O 

I 


I 




o 

I 


- 



90 
Sr 



95 
Zr 



103 
Ru 



106 
Rh 



125 
Sb 



131 

I 



132 



137 

Cs 



140 
Ba 



Fig. 4 Physical— chemical calculations for Small Boy. 



FALLOUT-PARTICLE GRADIENT STUDIES 

The condensed-state diffusion-limited model of fission-product absorption 
during fallout formation suggests that the concentration gradients of some 
radionuclides are very sharp. This is the resuit expected for radiocesium, for 
example. The importance of diffusion seems to be confirmed bv the cursor} 7 
experiment described in the following paragraph. 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 17 

Some large silicate fallout particles from shot Johnie Boy (supplied by 
USNRDL) were microscopically examined and divided into two sets, uncoated 
particles and iron- and lead-coated particles. Three particles were selected from 
the uncoated set for an experiment. Their gross appearance was that of a 
somewhat inhomogeneous, dark glass with obvious nodules of white material on 
the surface. Radii, r , were about 0.05 cm. The presence of radiocesium in the 
particles was established by gamma analysis using a multichannel analyzer and a 
1 37 Cs standard for reference. After the particles were leached for 1 hr with 19% 
MCI, no significant loss of cesium was observed. Leaching studies were then 
made using 5% HF with subsequent washing, drying at 110°C for 1 hr, gamma 
analysis, and weighing on a microbalance. Microscopic examination of the 
particles throughout this process showed a continuous, but not uniform, radial 
attack. The experiment was concluded when the specimens lost their integrity. 
Results obtained in this experiment are shown in Table 1. The relative average 

Table 1 

COMPOSITE 137 Cs PROFILES IN THREE 
JOHNIE BOY PARTICLES 



r/r n KC 



0.973 


3.4 


0.921 


1.8 


0.880 


1.6 



concentration, C, of cesium in the leached section is presented according to a 
calculated average radius, r, given by the weight loss. A concentration gradient is 
apparent in this table. Although this gradient, if we assume a uniform attack, 
seems small compared with the model calculations, it appears to support 
diffusion phenomenology. 

INTERACTIONS OF FALLOUT PARTICLES WITH THE ENVIRONMENT 

One of the most important properties of fallout is leachability. The chemical 
availability of fission-product nuclides to the biosphere is largely determined by 
this step. In general, the important variables in leaching are time, temperature, 
particle size, particle composition, the chemical nature of the leachant, degree of 
agitation, nature of the nuclide, and the leaching mechanism. The concentration 
gradient of fission products within the particle and the surface concentration of 
fission products are, of course, very important in establishing the leaching rate. 
Since this subject cannot be treated fully in this paper, treatment has been 
necessarily restricted to a few examples. However, it is emphasized that reliable 
prediction of the biological availability of fission products depends on an 
understanding of the diverse variables involved in leaching. The experiments 



18 NORMAN AND WINCHELL 

described here were performed in our laboratory. However, a large amount of 
pertinent information is reported in the literature, particularly in the glass and 
ceramics publications. For example, the studies of Douglas and El-Shamy 1 7 
indicate that leaching may occur by diffusion of the leachant through a 
silica-rich layer with protons or alkali ions occupying surface sites. Elliot and 
Auty, 18 investigating the leaching of borosilicate glasses containing fission 
products, proposed that a layer rich in silica and fission-product oxides was 
formed at the glass surface. They noted that the glass durability depended on 
cooling rate and reported the temperature dependencies of leaching. In several 
examples leaching of silicates appears to follow a desorption mechanism. 19 " 21 
Locsei described the importance of the degree of crystallinity in leaching of 
silicates. 

The removal of surface-adsorbed radionuclides may be considered the 
simplest step in leaching of fallout. In an experiment performed to study the loss 
of I from standard glass beads (National Bureau of Standards), tellurium 

dioxide was neutron irradiated in a Gulf General Atomic TRIGA reactor 
for 250 kw-hr and then allowed to decay for approximately 50 l 3 l Te half-lives. 
The sample was then heated, and the I, transpired by humidified oxygen, 

was absorbed on the 1.17- to 1.65-mm beads at near room temperature. The 
beads were transferred to a flask equipped with a charcoal trap, and the 
fractional loss of ' 3 1 1 from the beads in the laboratory atmosphere at room 
temperature was monitored by gamma analysis of the trap. The fractional release 
of 131 I as a function of time is shown in Fig. 5. Except for small, initial rapid 
release, the time dependence is linear with a loss of approximately 1% in about 
one week. The data are described well by 

F X 10 3 = 0.945 + 5.58 X 10" 2 t (1) 

where t is time (hours). The linearitv of the data in Fig. 5 is consistent with 
several possible release mechanisms, for instance, vaporization, vapor-phase 
transport, or reaction-rate control. 

It is concluded that appreciable amounts of adsorbed radioiodine may be 
lost to the atmosphere from fallout particles at room temperature during the 
half-life of 131 I. 

After the air-release experiment, the beads were leached with distilled water 
to simulate rain. At intervals a small aliquot was removed, gamma analyzed, and 
replaced in the container. A small volume of saturated KI was then introduced, 
and the leaching was again monitored at various periods. The data are shown in 
Fig. 6. A solution of KI is apparently a better leaching agent than H 2 since it 
provides a direct exchange for I - or a solubilizing agent for I 2 . Most of the 
sorbed iodine could be removed with a KI solution. 

Another study involved the leaching of radioiodine-doped glass with a 
composition of the 1450°K eutectic from the CaO-Al 2 3 -Si0 2 system. These 
data thus pertain to the special case of a refractory matrix containing 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 19 




80 100 

TIME, hr 

Fig. 5 Fractional release of surface adsorbed 
in laboratory air as a function of time. 



180 



by glass spheres at 298 K 



homogeneously distributed radioiodine. A portion of the glass was powdered, 
passed through a 100-mesh screen, and dried at approximately 100 C. Weighed 
samples were placed in double-thickness, No. 42 Whatman filter papers, which 
were supported in funnels equipped for aliquoting from the tip. Periodically 
5 ml of leachant were added after the previous leachant was drained, and the 
aliquot was made up to 50 ml and gamma analyzed with the use of reproducible 
geometry. Leaching was carried out at room temperature without agitation. 
Because of the low leaching rates, initial leaching times were about 20 min; the 
longest experiment lasted 2 days. 

The following four leachants were used: 



Leachant 



pH 



Remarks 



HC1 2 To represent the human stomach 

Tap water 8.3 Colorado River water 

Deionized water 7 To represent rain water 

NaOH 10 For comparison 



Although the adsorption characteristics of the paper may have been important, 
particularly in the deionized-water experiments, the effect was assumed to be 
negligible. Since a surface-area measurement has not been obtained for the 



20 



NORMAN ANDWINCHELL 




240 



1 31 



Fig. 6 Leaching of adsorbed I from glass spheres with distilled water and 

potassium iodide at 298 K as a function of time. 



prepared sample, the results can only be placed on a reciprocal weight basis at 
this time. By photomicrography the particles were found to be roughly 100 jd in 
"diameter." 

The leaching data are shown in Fig. 7. At first it was felt that the mechanism 
of leaching might be diffusion-limited transport of the leachant into the matrix 
or of radioiodine out through the matrix. If this were the case, since only 
about 1% of the activity was removed, leaching should be proportional to t 1 ^ 
(Fick's law). This dependence was not observed. However, the data can be 
described by the Elovich equation, which has found wide application in 
chemisorption: 



dQ 
dt 



a exp (— aQ) 



(2) 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 
6 



21 




t X 10" 2 , min 

Fig. 7 Leaching of radioiodine from powdered 1450 K eutectic CaO— 
Al 2 3 -Si0 2 doped with 131 I. 

where Q is the amount of material desorbed (sorbed), t is time, and a and a are 
constants at fixed temperature. By assuming that Q = when t = 0, we can write 
the integrated form: 



aQ= In (1 + aat) 



(3) 



The data can be fitted to Eq. 3 by using the values of a and a given in Table 2. 

The data fitted in this manner are shown in Fig. 8, where it is seen that their 
agreement with the Elovich equation is good. Leaching data reported by other 
laboratories 1 9_2 l can also be fitted to this equation. The fact that leaching data 
can be fitted to the Elovich equation, at least for short times, should be regarded 
as an empirical fact. 



22 



NORMAN AND WINCHELL 





i 


i 


>/ Tap 
y^# water 




- 




pH = 2 W 


t 

2 days 


- 


- 








- 


- 


//•/ pH 


= 10 




- 


20 


min >•/ 










\ 


/yY 




^ PH = 7 






c/ 








_ 


3 ^^ 




I 







LN (1 + aat), t in min 

Fig. 8 Leaching of radioiodine from powdered 1450 K eutectic CaO— 
A1 2 3 — Si0 2 . The data have been fitted to the Elovich equation (see text). 



Table 2 
COEFFICIENTS FOR THE ELOVICH EQUATION AT 300°K 





a 


x 10 2 , 


ttx io 3 , 


Leachant 


cp 


m/g/min 


(cpm/g)" 1 


Distilled water 




3.33 


2.33 


NaOH 




2.32 


1.25 


HC1 




8.77 


1.08 


Tap water 




6.62 


1.15 



To demonstrate further how a change in conditions can affect a change in 
mechanism, we performed a study of the leaching of sodium from a medium 
refractory glass. The matrix used for this study was purchased from the National 
Bureau of Standards in the form of glass spheres (Standard Reference Material 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 23 

1019). The composition of this glass is similar to that of window glass. A set of 
standard sieves was used to screen the sample, and four subsamples were chosen. 
These samples are described in Table 3. 

Table 3 
GLASS SAMPLES USED FOR LEACHING STUDIES 



Diameter, Number of 

Sample cm particles 

A 0.259 to 0.236 32 

B 0.236 to 0.165 39 

C 0.165 toO. 117 261 

D 0.117 to 0.089 530 



Before they were weighed, the samples were inspected for foreign material 
and were briefly washed with distilled water and dried. Irregular-shaped or 
inhomogeneous particles were discarded. After weighing, the samples were 
irradiated with neutrons in a Gulf General Atomic TRIGA reactor for 
250 kw-hr. A multichannel gamma analysis to 2 MeV showed peaks at 0.51, 
1.37, and 1.73 MeV which can be attributed to activated sodium (pair 
production, primary gamma, double escape from 2.75-MeV gamma) in the glass. 
The samples were placed in double-thickness, No. 44 Whatman filter papers, 
which were held in funnels equipped for aliquoting from the tip. Colorado River 
tap water with a pH of approximately 8.2 was used as the leachant. Periodically 
10 ml of leachant was added to the glass samples after draining of the previous 
aliquot, which was integrally gamma counted above 0.4 MeV. Leaching was done 
at room temperature without agitation. The pH of the leachant remained 
constant throughout the leaching periods. The overall leaching period was 
approximately 30 hr. 

The results are shown in Fig. 9, where the total amount of activity leached 
per particle is plotted as a function of the square root of the time. Referring to 
this figure, we see that samples B, C, and D exhibited a short lag period but that 
the early loss by sample A was rapid. After this lag period, the losses are all 
linear functions of the square root of the time. The results of a least-squares fit 
of the data to the equation 

Q=a + b/T (4) 

where Q is the amount of leached radioactivity per particle (counts per minute) 
and t is the time (minutes), are given in Table 4. From Table 4 and Fig. 9, the 
leaching mechanism for sample A appears to differ from that of the other three 



24 



NORMAN AND WINCHELL 




Fig. 9 Leaching of radioactivity from glass spheres by tap water as a function 
of the square root of the time. 



samples. This result is not understood. For samples B, C, and D, the square-root 
time dependence indicates a diffusion mechanism. As expected, the parameter b 
(cpm/min /2 in Table 4) increases with the particle surface area. These three 
samples also showed evidence of etching. The lag period may be attributed to an 
initially slow attack of the glass surface with respect to the interior, as was 
observed by Elliot and Auty. 1 8 

The fractional release of the radioactivity by samples B, C, and D may be 
considered on the basis of diffusion from a sphere with zero surface 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 25 

Table 4 
COEFFICIENTS IN EQ. 4 



a, 
cpm 


b, 
cpm/min i 


Mean particle 
radius, cm 


b/R 2 


11.8 


0.0644 


0.124 




-1.69 


1.64 


0.100 


164 


-2.83 


1.33 


0.071 


26.4 


-1.53 


0.689 


0.052 


25.5 



concentration. Since less than 1% of the activity was lost, this process is 



described by 



!(?)' 



(5) 



where f = fractional release 
R = radius 

D = diffusion coefficient 
t = time 

Radius-corrected leaching "rates" are presented in the last column of Table 4 as 
b/R 2 . Although it is not certain that sodium-ion migration is the rate-controlling 
process, these data suggest this to be the case. From these data and from initial 
specifications, the average value of D associated with a sodium-ion-migration 
mechanism was calculated to be 2.2 X 10 cm /sec. 

A different matrix would probably yield different results. As an example, 
Locsei 22 studied the leachability of a Na 2 0— CaO— MgO— A1 2 3 — Si0 2 system 
using 10% HC1. The character of the matrices ranged from 100% vitreous to 
100% crystalline. His data are described well by an equation of the form 

S = ae" bx (6) 

where S is the solubility (grams per square meter per day), x is the percentage of 
crystallinity, and a and b are constants. The effect of crystallinity was 
pronounced, being roughly two orders of magnitude in S. 

Another of our studies involved the leaching of recoil-loaded glasses. The 
recoil loading was done to simulate fallout containing high radionuclide 
concentrations near the particle surface as described by the Korts— Norman 
fallout model. 4 



26 



NORMAN AND WINCHELL 




Fig. 10 Fractional release of fission products from eutectic glass during 
leaching; the average uncertainty is 15%. 



Two silicate matrices were used, vitreous Nevada soil and the glass of 
1450°K eutectic composition from the CaO— Al 2 3 — Si0 2 system. The glasses 
were treated by heating them on flat platinum surfaces for several hours at 
1400 C in air. A small piece of fully-enriched uranium foil was placed between 
the two flat glass surfaces when they had cooled, and the sample was irradiated 
with neutrons in a Gulf General Atomic, Inc., TRIGA reactor for 125 kw-hr. 
The radioactivity was allowed to decay for approximately 5 days. Then the 
glasses were separated from the foil and were lightly cleaned with fine 
carborundum paper to eliminate spalled uranium and fission products from the 
surfaces. After being cleaned and dried, the samples were subjected to leaching 
at room temperature in plastic beakers containing 5 ml of a slurry of 11.5 g of 



PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 



27 



3 - 





D, 131 l 


I 

V, 


147 Nd 


I 




p 




A,"Tc 


• . 


143 Ce 










A, 140 Ba 


O, 


140 La 




/ D 






O , 132 Te 






D / 
















So 


6 


— 










/s 


£r 


- 




I 




i 




- 



1 - 



Fig. 11 Fractional release of fission products from Nevada glass during 
leaching; the average uncertainty is 25%. 



montmorillonite in 750 ml of distilled water. The clay was used to provide an 
efficient sink for leached fission products. During leaching both the glasses and 
the leaching slurries were separately analyzed with a 4096-channel gamma 
analyzer equipped with a lithium-drifted germanium detector. The gamma 
spectra were then corrected by referring them to the irradiation time using the 
pertinent half-lives. Several nuclides were found in all spectra for the leaching 
slurries and for both glasses. 

The data are shown in Figs. 10 and 11, where the fractional releases of the 
glasses are plotted as functions of the square root of the time. From these figures 
the leaching process appears to be one of diffusion during the leaching period of 
132 min. Several qualitative conclusions may be made concerning these data. 



28 NORMAN AND WINCHELL 

Since the fractional releases are not highly correlated with mass number (recoil 
ranges are highly correlated with mass), the leaching process is not totally 
dependent on the recoil distribution of fission products. The approximate 
leaching penetration during the experiment can also be calculated. Assuming a 
recoil range of 10 fj. for a nuclide in the eutectic glass and using a fractional 
release value of 5 X 1(X 3 for this nuclide, we calculate a penetration distance of 
approximately 200 A. Thus for volatile chains the degree of surface loading can 
play a dominant role in subsequent leaching. In the present study leaching rates 
differ by up to a factor of about 4 for all the nuclides studied in the two glasses. 
The reason for differences between nuclides is not known, but, if diffusion is 
rate controlling, such differences are expected. It is also observed that the order 
of leaching rates of different nuclides from the eutectic glass differs from that of 
the Nevada glass, and, surprisingly, the leaching rates are only slightly different 
for the two glasses. This is consistent with the similarity of these two glasses in 
high-temperature diffusion studies. 

Considering the studies reported in this section, it appears unlikely that any 
a priori unified scheme of transfer of radionuclides from fallout particles to the 
biosphere can be established now. Such a scheme would require the output of a 
model such as Korts and Norman have described. It would also require a good 
physical— chemical model involving chemical attack on fallout particles and 
migration of radionuclides in many environments. This latter task is formidable. 
It is not true that simple models to describe leaching of fallout should not be 
devised. This is exactly what should be done. However, these simple models 
should strive for as much realism as possible, and, in view of our present 
knowledge, we are quite limited, particularly in the leaching model. 



ACKNOWLEDGMENT 

This work was supported by the Department of the Army, Office of Civil 
Defense, under Contract DAHC20-70-C-0388. 

REFERENCES 

1. E. C. Freiling, Fractionation. I. High-Yield Surface Burst Correlation, Report USNRDL- 
TR-385, U. S. Naval Radiological Defense Laboratory, Oct. 29, 1959. 

2. E. C. Freiling, G. R. Crocker, and C. E. Adams, Nuclear-Debris Formation, in 
Radioactive Fallout From Nuclear Weapons Tests, Proceedings of the Second Confer- 
ence, Germantown, Md., Nov. 3-6, 1964, A. W. Klement (Ed.), AEC Symposium Series, 
No. 5 (CONF-765), pp. 1-43, 1965. 

3. C. F. Miller, Fallout and Radiological Countermeasures. Volume E, Report AD-410522, 
p. 26, Stanford Research Institute (Project No. IM-4021), 1963. 

4. R. F. Korts and J. H. Norman, A Calculational Model for Condensed State Diffusion 
Controlled Fission Product Absorption During Fallout Formation, Report GA-7598, 
General Dynamics Corp., General Atomic Div., Jan. 10, 1967. 






PHYSICAL, CHEMICAL, AND RADIOLOGICAL PROPERTIES 29 

5. E. C. Freiling, Mass-Transfer Mechanisms in Source-Term Definition, in Radionuclides in 
the Environment, Advances in Chemistry Series, No. 93, pp. 1 — 12, American Chemical 
Society, Washington, D. C, 1970. 

6. M. W. Nathans, R. Thews, and I. J. Russell, The Particle Size Distribution of Nuclear 
Cloud Samples, in Radionuclides in the Environment, Advances in Chemistry Series, 
No. 93, pp. 360-380, American Chemical Society, Washington, D. C, 1970. 

7. R. C. Tompkins, I. J. Russell, and W. N. Nathans, A Comparison Between Cloud 
Samples and Close-in Ground Fallout Samples from Nuclear Ground Bursts, in 
Radionuclides in the Environment, Advances in Chemistry Series, No. 93, pp. 381—400, 
American Chemical Society, Washington, D. C, 1970. 

8. R. E. Heft, The Characterization of Radioactive Particles from Nuclear Weapons Tests, 
in Radionuclides in the Environment, Advances in Chemistry Series, No. 93, 
pp. 254—281, American Chemical Society, Washington, D. C, 1970. 

9. J. H. Norman, Henry's Law Constants for Dissolution of Fission Products in a Silicate 
Fallout Particle Matrix, Report GA-7058, General Dynamics Corp., General Atomic 
Div., Dec. 29, 1966. 

10. P. Winchell and J. H. Norman, A Study of the Diffusion of Radioactive Nuclides in 
Molten Silicates at High Temperatures, in High Temperature Technology, Proceedings of 
the Third International Symposium, Asilomar, Calif., Sept. 17, 1967, p. 479, Butter- 
worth & Co. (Publishers) Ltd., London, 1969. 

11. C. F. Adams, J. T. Quan, and W. R. Balkwell, High Temperature Measurements of the 
Rates of Uptake of Molybdenum Oxide, Tellurium Oxide, and Rubidium Oxide Vapors 
by Selected Oxide Substrates, in Radionuclides in the Environment, Advances in 
Chemistry Series, No. 93, pp. 35 — 62, American Chemical Society, Washington, D. C, 
1970. 

12. F. W. Bloore, K. F. Benck, D. A. Furcy, P. C. Harris, B. L. Houseman, and L. A. Walker, 
The Mechanisms of Fallout Particle Formation, Annual Progress Report for Period 
Ending April 1969, Report NDL-SP-36, U. S. Army Nuclear Defense Laboratory, 1969. 

13. I. J. Russell, fundamental Studies in Fallout Formation Processes, Progress Report, 
June 1, 1967, to May 31, 1968, USAEC Report NYO-3756-2, Boston College, June 1, 
1968. 

14. S. Z. Mikhail, Beta-Radiation Doses from bailout Particles Deposited on the Skin, this 
volume. 

15. J. H. Norman, P. Winchell, H. G. Staley, M. Tagami, and M. Hiatt, Henry's Law Constant 
Measurements for Fission Products Absorbed in Silicates, in 'Thermodynamics of 
Nuclear Materials, 1967, Symposium Proceedings, Vienna, 1967, p. 209, International 
Atomic Energy Agency, Vienna, 1968 (STI/PUB/162). 

16. J. H. Norman, P. Winchell, J. M. Dixon, B. W. Roos, and R. F. Korts, Spheres: 
Diffusion-Controlled Fission Product Release and Absorption, in Radionuclides in the 
Environment, Advances in Chemistry Series, No. 93, pp. 13 — 35, American Chemical 
Society, Washington, D. C, 1970. 

17. R. W. Douglas and T. M. M. El-Shamy, Reactions of Glass with Aqueous Solutions, ./. 
Amer. Ceram. Soc, 50: 1-8(1967). 

18. M. N. Elliot and D. B. Auty, The Durability of Glass for the Disposal of Highly 
Radioactive Wastes: Discussion of Methods and Effect of Leaching Conditions, (Uass 
Technol., 9: 5- 1 3 ( 1968). 

19. J. Ralkova and J. Saidl, in Treatment and Storage of High- Lev el Radioactive Wastes, 
Symposium Series, Vienna, 1962, p. 347, International Atomic Energy Agency, Vienna, 
1963 (STI/PUB/63). 

20. R. Bonniaud, C. Sombret, and F. Laude, in Treatment and Storage of High-Level 
Radioactive Wastes, Symposium Series, Vienna, 1962, pp. 366—368, 372—373, Inter- 
national Atomic Energy Agency, Vienna, 1963 (STI/PUB/63). 



30 NORMAN AND WINCHELL 

21. W. E. Clark and H. W. Godbee, in Treatment and Storage of High-Level Radioactive 
Wastes, Symposium Series, Vienna, 1962, p. 430, International Atomic Energy Agency, 
Vienna, 1963 (STI/PUB/63). 

22. B. P. Locsei, Acid Resistance of Vitroceramic Materials on a Feldspar-Diopside Base, in 
Symposium on Nacleation and Crystallization in Glasses and Melts, p. 71, American 
Ceramic Society, Columbus, Ohio, 1962. 

23. j. Crank, The Mathematics of Diffusion, p. 87, Oxford University Press, London, 1956. 



BETA-RADIATION DOSES FROM FALLOUT 
PARTICLES DEPOSITED ON THE SKIN 



S. Z. MIKHAIL 

Environmental Science Associates, Burlingame, California 



ABSTRACT 

Absorbed beta-radiation dose expected from fallout particles deposited on the skin was 
estimated by use of the Beta Transmission, Degradation, and Dissipation (TDD) model. 
Comparison of computed doses with the most recent experimental data relative to skin 
response to beta-energy deposition leads to the conclusion that, even for fallout arrival times 
as early as 10 sec (16.7 min postdetonation), no skin ulceration is expected from single 
particles 500 u or less in diameter. 

Doses from arrays of fallout particles of different size distributions were computed also 
for several fallout-mass deposition densities; time intervals required to accumulate doses 
sufficient to initiate skin lesions were calculated. 



In 1954 residents of Rongelap Atoll in the Marshall Islands were exposed to 
fallout arriving within hours after detonation of the Castle Bravo nuclear 
device. Several of the atoll's inhabitants suffered severe skin burns. Primarily as a 
result of this experience, the possibility of "beta burn" from nuclear fallout has 
been recognized. However, to date, attempts to predict the acute or chronic skin 
effects that might be expected following exposure to fallout have been limited. 
This limitation results mainly from the lack of experimental data on the biologic 
response of the skin to particulate-source exposures, from incomplete under- 
standing of the relation of such response to that encountered in other localized 
exposures (e.g., collimated X-ray beams) for which data are available, and from 
the absence of reliable beta-dose calculational models. All these are required to 
relate dose to observed effect in a manner allowing prediction of the biological 
effects from knowledge of the expected fallout interaction. 

The literature indicates that work on the theoretical aspects of the beta-dose 
problem has progressed faster than have experimental efforts. As early as 1956 
Loevinger, Japha, and Brownell devised an analytical representation (model) to 
calculate beta doses from "discrete radioisotope sources." 1 By 1966 four models 

31 



32 MIKHAIL 



were available. The most precise, though complex, of these models is the 



Transmission, Degradation, and Dissipation (TDD) model. This paper is based 
on the TDD model and presents predicted beta doses that would result from skin 
deposition of nuclear-weapon fallout particles. 

A nuclear attack on the United States would be expected to result in 
low-intensity gamma-radiation fields over much of the fallout area that would 
develop. Exposure to the low-intensity field would pose little or no immediate 
or long-term whole-body gamma-radiation hazard. However, it has been 
suggested that in such situations contact of individual fallout particles with 
exposed skin could constitute a potential hazard. Individual particles can deposit 
on the skin via direct deposition during passage of the fallout cloud or following 
resuspension of particles at a later time. 

Each particle, if radioactive enough, is capable of producing a lesion. If 
several particles reside close enough in the same general skin area, their effects 
could be additive, in the sense of causing one lesion. However, at larger 
particle-separation distances, beta-radiation dose deliveries would not interact. 
That is, the dose contribution from one particle to the tissue in the vicinity of 
another particle would be negligible. This situation is treated separately in the 
next three sections. At small particle-separation distances, estimation of the dose 
delivered at any point in tissue would require summation of the dose 
contributions from all particles in the immediate vicinity. This latter situation is 
treated separately also. 

THE SINGLE-PARTICLE BETA-DOSE MODEL 

The TDD model for single particles is composed of six separate semi- 
independent computer codes. The first (Code 1) is a nuclide-abundance code 
that calculates the activity of each radionuclide generated in the detonation of a 
nuclear device or weapon. This code also considers radioactive decay and 
calculates fission-nuclide activity at any postdetonation time. 

Code 2 computes the beta spectrum for each beta-emitting nuclide, given the 
end-point energies, beta branching fractions, and degree of forbiddenness of the 
beta transitions. 3 Output from this code is a sequence of values representing the 
probability that a beta particle will be emitted with an energy between E and 
E + AE, where AE = 0.04 MeV and values for E range from to the maximum |3 
energy, E max . Individual fission-product beta spectra have been generated and 
are stored on tape for use with the composite-spectrum code (Code 3). 

Code 3 is a composite-spectrum routine that sums the individual beta spectra 
of the fission-product nuclides with appropriate weighting for the activity of 
each contributing nuclide, as determined by Code 1. Code 3 produces a 
point-source beta spectrum at a given time for the specific weapon under 
consideration. Output from this code is a sequence of values representing the 
number of betas per energy interval emitted by the source. 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 33 

The electron spectrum from a fallout particle (assumed to be spherical in 
shape) differs from that produced by a point source because scattering and 
absorption processes within the particle degrade the spectrum. Calculation of the 
extent of degradation is complicated by the fact that in fallout particles some 
fission products are uniformly distributed within the particle material, others 
have condensed on the particle surface, and the rest behave in an intermediate 
fashion. 4 

Korts and Norman developed a model, 5 termed the Condensed State 
Diffusion Controlled Model, which describes the mechanism of fission-product 
absorption in fallout material distributed in a radioactive cloud following a 
nuclear detonation. In this model they assumed that (1) the fallout material is 
glassy silicate; (2) the surface of a fallout particle is in equilibrium with the gas 
phase; and (3) the rate of transfer of fission products into the interior of the 
fallout particle is diffusion controlled. One output of this Condensed State 
Diffusion Controlled Model consists of a set of radial fission-product-concentra- 
tion profiles in fallout particles of different sizes. Using such concentration 
profiles, Korts and Norman calculated for each fission product the percentage of 
total nuclide present which would diffuse into the particle. In almost all cases 
examined, they found that "loadings" of 0, 25, 50, 62.5, 75, 82.5, and 100% 
(by weight) could be used to describe the portion of fission product present 
diffusing into the particle. (The complementary percentage in each of the seven 
classes represents the portion of the fission product present that remains at the 
particle surface.) Zero percent diffusion takes place when the fission product 
condenses on the particle surface, essentially without any diffusion during 
particle cooling; whereas. 100% diffusion represents complete diffusion leading 
to homogeneous distribution of the fission product in the silicate matrix. This 
Condensed State Diffusion Controlled Model was used in the manner described 
in the following paragraph to provide the geometric basis for the electron 
degradation within fallout particles. 

Degradation suffered by the emanating electron spectrum is handled by 
Code 4, a Monte Carlo program that starts with a given number of emitted betas 
in a specified energy interval and then computes the loss in electron energy and 
number due to scattering and absorption processes within the particle. The code 
outputs two sets of Monte Carlo determined energy-dependent loss coefficients, 
set A for homogeneously distributed fission products and set B for surface- 
condensed fission products. These coefficients are then applied to the composite 
beta spectrum from the point source of fission products (Code 3) by Code 5. 
Application of these loss factors is straightforward for the and 100% diffusion 
cases (in which set B and set A, respectively, are utilized). For five intermediate 
diffusion cases, set A was applied to the percentage diffusing into the particle, 
and set B was applied to the percentage remaining at the surface. Output of 
Code 5 thus consists of a degraded beta spectrum emerging from a fallout 
particle of a specified size. 



34 MIKHAIL 

Code 6 operates on the resulting composite degraded spectrum to com- 
pute the depth-dose rate in tissue. This is based on energy-dissipation factors 
for fast electrons as calculated by Spencer. 

The dose rate, D t (in rads per hour), at a tissue depth Z centimeters from a 
particle of volume V (in cubic centimeters) emitting N e (E ) beta particles per 
second per cubic centimeter in the energy interval AE with mean energy E (in 
million electron volts) (this is the emerging degraded spectrum in the present 
work) is given by: 



kfffV v 1 Eo = E rnax -AE/2 

^rS^ffi J(x) (dE/dr) Eo N e (E ) (1) 



where k = a constant, 5.76 X 10 5 (rad-g-sec)/(MeV-hr), relating energy- 
transport rate to dose rate 
f = dimensionless correction factor for a semi-infinite absorber, deter- 
mined from an auxiliary Monte Carlo program 
g = ratio of dose rate at a distance Y (in centimeters) from the center of 
a spherical source (radius R in centimeters) to the dose rate from a 
point source at the same distance (Y>R); the ratio is a 
dimensionless quantity given by 



£ [« • (^f) - (m) 



(2) 



J(x) = Spencer's energy-dissipation-distribution function evaluated at tis- 
sue depth Z measured in units of the normalizing residual range, r ; 
x = zp/r , p being the density of the absorbing medium 6 
(dE/dr)£ Q = stopping power of the absorber for electrons emitted from the 
particle with energy E 

The resulting dose rates, summed over the composite degraded spectrum, 
form the output of this part of the model. 

The final operation of the composite TDD model integrates the various dose 
rates (from each energy interval) computed via Eq. 1 over time to get the total 
absorbed dose. In practice, to reduce computation time, we carry out the 
integration by the use of time-integrated beta activities derived from the 
inventory code (Code 1) to make up a time-integrated composite beta spectrum. 
This spectrum is then degraded and deposited in tissue as explained previously; 
i.e., the time integration is done from the start rather than as the last step. 

Recently the six codes have been unified into a single modified composite 
program to reduce computer run time. 7 Also, several new features have been 
introduced into the composite program to increase its ability to cope with a 
variety of beta-dose problems. 8 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 



35 



EVALUATION OF THE SINGLE-PARTICLE MODEL 

Validity of the TDD-model dose predictions has been examined 8 by 
comparing the model-computed doses delivered by reactor-irradiated UC 2 
particles with (1) doses from the UC 2 particles measured with a ^-extrapolation 
chamber; 9 (2) values for UC 2 particle dose obtained by a photographic-film 
dosimetry technique; and (3) dose values computed by applying a completely 
independent Monte Carlo calculational technique. 

Tests included doses at shallow as well as at relatively large depths (7500 /i) 
in tissue and at points directly underneath the particle and points radially 
displaced to distances as far as 5000 jLt. Particles of variable sizes and reactor 
irradiation times of different duration were also included in the comparisons. 




125 230 250 

PARTICLE CORE DIAMETER, » 

Fig. 1 Ratio of calculated (TDD model) dose to dose measured with a 
/^-extrapolation chamber (tissue depth, 30 ju). 



Typical results obtained in the comparisons with data from the extrapolation 
chamber, the Monte Carlo program, and the photographic-film exposure 
technique are presented in Figs. 1, 2, and 3, respectively. The primary 
conclusions drawn from the comparisons were: 8 

1 . On the whole, agreement between values obtained by use of the composite 
program and those obtained by experimentation and exercise of the cited Monte 
Carlo program was satisfactory. 



36 



MIKHAIL 



10 J x- 



1 r 



i I f 



i ( 



i i r 



O, Extrapolation chamber 
x, TDD model 

+, Monte Carlo, surface detector 
~L, Monte Carlo, volume detector 




1000 2000 3000 4000 5000 

TISSUE DEPTH, pi 



6000 



7000 Y 8000 

+ 



Fig. 2 Comparison of TDD model calculations with Monte Carlo calculations 
and extrapolation-chamber measurements (delay time, 5.75 hr). 



2. The ranges of particle sizes (85 to 310 jU) and time periods of reactor 
irradiation (5 min to 24 hr) considered appear to have little influence on the 
extent of agreement achieved. 

3. Tissue beta-radiation delivery (i.e., absorption) estimated by the com- 
posite TDD model for shallow tissue depths is invariably higher than that derived 
from the Monte Carlo calculations. As the tissue depth considered increases, 
agreement between the TDD model and experimental results improves until, as 
shown in Fig. 4, at a tissue path length of about 4000 id the values for the model 
and those for the test method tend to agree. Such relations are interpreted to 
indicate that the model underestimates electron attenuation in the particle 
material and overestimates that in tissue. 

4. Delay times (time periods between termination of reactor irradiation and 
start of tissue exposure) greater than approximately 25 hr appear to increase the 
difference between model predictions and values determined by the test 
methods, but not to an appreciable degree. 

5. Doses measured directly below the particle by photographic-film experi- 
ments agree rather well with model predictions, except for dose locations very 
close to the particle, in which case apparent saturation of film occurs. 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 



37 



10' 



10 



10" 1 



i r 



O, Film data 
x, TDD model 




100 



200 



300 400 

DEPTH, mg/cm 2 



500 



600 



700 



Fig. 3 Comparison of calculated (TDD model) dose rates with film data 
(160-yu particles). 



DOSE CRITERIA FOR SINGLE-PARTICLE EXPOSURE 



Serious acute lesions of the skin are induced primarily by the destruction of 
the germinal cells of the epithelium. In humans the subsurface depth of the skin 
germinal-cell layer varies from 20 to 250 jd. However, for convenience a single 
depth of 100 id is usually chosen to represent the critical level. The absorbed 
beta dose (or amount of beta energy absorbed in an infinitesimally small mass of 



38 



MIKHAIL 



25 



w < 
< 



1.6 


I 


I I I 


I I I I I 


I I I 


1.4 


3 









1.2 
1.0 


J 







§ 


o- 


0.8 


— 







8" 


0.6 


I 


I I I 


I I I I I 


i i r 



300 



1500 2700 3900 5100 

TISSUE DEPTH, \i 



6300 



7500 



Fig. 4 Ratio of model (TDD) dose to extrapolation-chamber dose, as a 
function of tissue depth (2 36-/i particles). 



tissue surrounding the point of interest) at a point 100 jjl deep "underneath" the 
source (fallout particle) is termed the "point depth dose" at 100 ju. 

For a considerable period of time, beta-radiation damage to skin was viewed 
almost entirely in terms of the estimated 100-ju point depth dose. However, in 
recent years it has become generally accepted that for a serious radiation lesion 
to occur the germinal cells must be destroyed over an area of skin too large for 
normal regeneration to replace them within a reasonable period of time. Of 
necessity this has led to consideration of area dose absorption rather than dose 
absorbed at a specific point. 

A survey by Krebs 1 in 1967 showed that, for an acute lesion of the skin to 
develop, the viable germinal cells must be reduced to a survival level of less than 
0.001 over an area sufficiently large to prevent replacement of dead cells via cell 
proliferation in the margin of the exposure field. Tne criterion recommended by 
Krebs is that a 1500-rad or greater dose to the skin, deposited on the periphery 
of a 4-mm-radius circular field 100 fd deep in tissue, constitutes a potential 
skin-damage threat. 

Krebs derived his conclusions from X-ray microbeam studies. At the time of 
his evaluation, few biological-damage data were available from single-particle 
investigations. After Kreb's conclusions were published, an experimental study 
testing the suggested criterion was conducted. 1 l Irradiated microspheres were 
used as radiation sources, and swine were the experimental animals. Results 
obtained in this study showed that the minimum radiation dose, deposited at the 
periphery of a 4-mm-radius field, required to produce a very small ulcer (less 
than 0.5 mm in diameter) is estimated to be below 405 rads. An ulcer 1 mm in 
diameter was produced by absorption of 660 rads (same field), a 2-mm-diameter 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 39 

ulcer by about 1150 rads, etc. If we assume linearity of the ulcer diameter with 
dose (4-mm-radius field), as indicated by the data, then by extrapolation a 
350-rad delivery would be sufficient to yield a zero-diameter ulcer. 

In this work the 660-rad dose was used as the threshold dose for damage to 
human skin from deposited fallout particles. This admittedly arbitrary threshold 
was chosen on the basis that a 1-mm-diameter ulcer is small enough to be 
considered a threshold for damage but large enough to be recognizable. Choice 
of 350 or 1150 rads as a threshold dose does not appreciably affect the 
conclusions derived. 



THE MULTIPLE-PARTICLE BETA-DOSE MODEL 

The multiple-particle beta-dose model is designed for evaluation of dose 
situations in which the fallout-particle deposition density on the skin is of such 
magnitude that beta radiation emitted from adjacent particles is absorbed in the 
same tissue volume. 

Two distinct approaches can be used to examine the absorbed dose from 
multiparticle sources. In the first the source is viewed as a uniform plane source 
of strength dependent only on the number of "equivalent fissions" of fission 
products deposited per unit area. In the more realistic second approach, the 
source is taken to be a group of fallout particles of size distribution dependent 
on the weapon yield and the distance from ground zero to the deposition point 
of interest. The beta dose delivered by such a source to the skin depends, in 
addition to the particle-size distribution, on the fallout mass deposited per unit 
area and on the specific activity of the fallout. 

The plane-source approach was pursued by Brown, who used Spencer's 
plane-source calculations to compute beta-dose-rate multipliers for each fission- 
product beta emitter. Brown considered two situations: (1) contact dose, where 
the plane source lies between an absorbing medium and a backscatterer, and (2) 
beta bath, where an attenuation medium separates the absorbing medium from 
the plane source. 

Using Brown's contact-dose multipliers and the output from the abundance 
code (Code 1) of the TDD program, we can calculate the dose delivered to the 
skin from a plane source of the desired activity level. Results of these 
computations are considered later. 

In the second, or particulate, model, the source is viewed, for purposes of 
analytical examination, as consisting of superimposed strata of fallout particles, 
each stratum being in contact with the skin surface. Each stratum consists of an 
array of equal-size particles with separate particles placed at the intersections of 
a uniform rectangular-plane grid. Figure 5 illustrates the concept. The dose is 
estimated at point X, 100 jU below the central point of the grid plane. The dose 
at X can be determined by summation of the dose contributions from individual 
particles as computed by the TDD model. 



40 



MIKHAIL 




Fig. 5 Schematic of the multiple-particle array concept. 



Dimensions of the unit cell of the grid are determined by the mass 
deposition density (in grams of fallout per square foot) and the size class of 
particles forming the grid. For a relatively large array of closely spaced particles, 
the dose at any point 100 /jl below the plane becomes very close to the dose at 
X. 

For calculation of the dose at X, dose contributions from the particles 
closest to X are computed and added. Then doses from particles at increasing 
distances from X are added until the incremental increase in dose falls below a 
predetermined fraction of the initial sum. at which time the calculation stops. 

For accuracy, 10 strata of arrays were considered in the calculations. Each 
stratum was assumed to contain 10% of the total fallout mass deposited (on a 
unit-area basis). Particle sizes for the arrays were determined by the following 
procedure: 

1. Assume a mean and a maximum particle size for the fallout deposit. In the 
first four situations considered, take the means parametrically as 100, 250, 500, 
and 700 id each with a fixed maximum of 1000 fd. In a fifth case take the mean 
as 1000 and the maximum as 2000 fi. 

2. Assuming a log-normal distribution 4 of particle sizes in each case, and 
with the knowledge of the maximum and the mean, trace a log-probability line 
for the particle-size distribution. 

3. Subdivide the line into 10 equal-probability regions and determine for 
each region the particle size, corresponding to the midrange probability. Use 
these 10 mean particle sizes for the strata. 

Two facts are worth mentioning here. (1) For obvious reasons, the 
particulate approach is much more realistic than the plane-source approach. (2) 
For the same number of equivalent fissions per unit area, the plane-source 
computations give dose values higher than the Multiparticle Model by as much as 
an order of magnitude (see Fig. 6). The discrepancies are apparently chiefly due 
to attenuation within particles. The detailed differences between the dose values 
resulting from the two approaches depend on the particle-size distribution 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 



41 



10 E 



10 4 



10' 



10° 



I I 


III I I I I I I III- 


^^_^- 


- 


— Plane source 


- 


""* Particulate source — 




Mean particle diameter, 100 /u 




Maximum particle diameter, 1000 m 


. 


- 


— "" Particulate source 


^*« 


Mean particle diameter, 500 ju 


I I 


Maximum particle diameter, 1000 u _ 

III > I I I I I III 



10 1 10 2 

RETENTION TIME, hr 



10 



Fig. 6 Comparison between doses computed for a plane source and the 
corresponding values for a multiparticle source. Tissue depth, 100 m ; delay time, 
10 sec-, deposition density, 100 mg/sq ft; activity, 10 fissions/cc. 



assumed in the particulate approach (Fig. 6). For a fixed maximum size, the 
difference decreases as the mean particle size decreases, but a factor of 5 was the 
smallest encountered for the cases considered. 



DOSE CRITERIA FOR MULTIPLE-PARTICLE DEPOSITION 



To date no criterion has been explicitly proposed for skin damage from 
multiple particles. However, the following points serve as guidelines for 
establishing such a criterion: 

1. As in the case of single-particle sources, damage to the skin will occur 
when the survival level of the germinative cells is reduced to less than 0.001 over 
an area sufficiently large to preclude replacement of dead cells via prolifera- 
tion. 10 

2. Such a reduction in survival occurs at a lower dose level from a 
multiparticle source than from a single-particle source. Krebs estimates that a 
uniform 1300-rad dose from a multiparticle source would cause the same 
reduction in survival level brought about by a 1500-rad dose from a 
single-particle source. 1 3 



42 MIKHAIL 

3. In view of the difference between the predicted single-particle critical dose 
(1500 rads) and the corresponding experimentally determined value of 660 rads, 
an adjustment has to be made to the suggested multiple-particle value to bring it 
into line with experiment. 

4. It seems reasonable to accept a proportional dose for the multiparticle 
situation; i.e., (1300/1500) X 660 ~ 570 rads. That is, exposure of the skin 
(100-jU depth) to a uniform deposited dose of 5 70 rads from a multiple source 
will be assumed sufficient to damage the skin in the manner described for the 
single-particle exposure. 



RESULTS AMD DISCUSSION 

Doses from Single Particles 

Point depth doses (estimated at 100-/J tissue depth directly below the fallout 
particle) and Krebs doses (estimated at a point radially displaced 4000 jU in a 
plane 100 jd below the skin surface) were computed for particles 50, 100, 200, 
500, 750, and 1000 jU in diameter; for each particle size, doses were computed 
for 10 ,10 , 10 , and 10 6 sec of delay time (time between weapon detonation 
and deposition of the particle on the skin). The fallout particles were assumed to 
contain 10 1 ' fissions per cubic centimeter. For all but exceptional situations, 
10 1 ^ fissions/cc is considered the maximum expected fallout activity. Beta doses 
from fallout of higher fission density can be obtained from the values reported 
here by linear extrapolation. 

Figures 7 to 10 present samples of the computer-plotted doses as functions 
of particle retention time on the skin. It can be seen from Fig. 7, which presents 
Krebs doses for the earliest particle arrival time considered, that single fallout 
particles smaller than 500 fj. in diameter, landing on the skin as early as 10 sec 
(16.7 min) after detonation, will not cause any skin burns. A single 500-jU 
particle arriving even this early has to be retained about 10 hr before it delivers 
the 660 rads required for damage. Table 1 shows experimental data obtained at 
Oak Ridge National Laboratory (ORNL) for expected retention times of 
particles on human skin under normal conditions of temperature and humid- 
ity. 14 Considering the values in Table 1, even a 500-jU particle would obviously 
be incapable of producing a 1-mm lesion. 

Figure 8 presents the point depth doses delivered by the same particles under 
the same (early arrival) conditions. Comparison of Figs. 7 and 8 shows that point 
depth doses are higher than the corresponding Krebs doses by a factor of 10 to 
10 3 depending on the particle size. Lower ratios correspond to larger particle 
sizes. 

From Figs. 9 and 10, it can be seen that, after a delay of a little over 10 sec 
(about 2.8 hr), even a 1000-jU particle can be tolerated, provided its retention 
time does not exceed its expected value in Table 1. 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 



43 



10 : 



10- 



10 1 



10 l 



10" 1 



10' 



I III 


! 1 1 | 1 


I 


i i- 


_ 


Particle diameter 


M 




1000 






= ■ " 


7^0 




- 




— 


^nn 




— 


: ^^~ . — ■ 




660 rads_ 


- 






— 


1 


°00 




: 




~ 






— 




— 


*n 




— 




1 III 


I I I I I I 


; 


I I 



10' 10' 

RETENTION TIME, hr 



10 



Fig. 7 Krebs dose delivered to the skin by single fallout particles at an 
exposure starting time of 10 sec after detonation. Tissue depth, 100 \i. 




RETENTION TIME, hr 



Fig. 8 Point depth dose delivered to the skin by single fallout particles at an 
exposure starting time of 10 sec after detonation. Tissue depth, 100 \i. 



44 



MIKHAIL 



10' 



10 



10- 



10 



10 L 



10" 



10" 



- 


! Particle diameter, u. ' I — 
1 ooo - 


^^^ 


"""*""""" ____ 750 


^^-—- -^~^~ 


~^_ _6_50_rads~ 
500 


-^ 


- 


_ 


. 200 


— ^^--^^^ 


— 




— mn 


- ^^^^ 


- 




Rn 


— ^ "" 




I I 


! i i i i I i ; i i 



10 l 



10 1 10 : 

RETENTION TIME, hr 



10' 



Fig. 9 Krebs dose delivered to the skin by single fallout particles at an 
exposure starting time of 10 sec after detonation. Tissue depth, 100 ju. 



10' 



Particle diameter, \i 
1000 




RETENTION TIME, hr 



Fig. 10 Krebs dose delivered to the skin by single fallout particles at an 
exposure starting time of 10 sec after detonation. Tissue depth, 100 u. 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 45 



Table 1 

EXPECTED RETENTION TIMES OF 
PARTICLES ON HUMAN SKIN* 



Particle diameter, ju 


Time, hr 


50 




6.8 


100 




3.5 


200 




2.7 


500 




2.2 


75 




2.1 


1000 




2.0 


* From Ref. 


14. 





Figure 10 shows further that, after a delay of 10 5 sec (about 28 hr), no 
single particle of any size can possibly cause a beta burn (except for the 1000-jU 
particle retained for an inordinately long time). 



Doses from Multiparticle Fallout 

Samples of the data computed with the Multiparticle Model are shown in 
Figs. 11 to 15. In these figures time-integrated doses from fallout deposition 
densities of 100, 200, 500, 1000, 2000, and 5000 mg/sq ft for different 
particle-size distributions have been plotted as functions of fallout retention 
time. All computations are based on 10 fissions/cc. Delay times of 10 , 10 , 
10 5 , and 10 6 sec are covered. 

Figure 11 shows that for a delay time of 10 sec even the lowest deposition 
density (100 mg/sq ft) of particles of 100-ju mean diameter and 1000-jU 
maximum diameter (size distribution A) can deliver to the skin in less than 1 hr 
more than the 5 70 rads required for damage in the multiparticle situation. 
However, as seen in Fig. 12, the same mass of fallout of 1000-jU mean diameter 
and 2000-/J maximum diameter (size distribution B) delivers a maximum of only 
300 rads, even if retained over 100 hr. Other size distributions give intermediate 
doses. 

The situation changes somewhat at the next higher fallout-arrival (delay) 
time, 10 sec. A 200 mg/sq ft deposit of size distribution A can be tolerated in 
this case for about 1.5 hr (Fig. 13). 

After a delay of 10 sec, a 2000 mg/sq ft deposit of size distribution A gives 
the critical 570 rads in about 1.5 hr (Fig. 14); after a delay of 10 6 sec (11.5 
days), it takes 5000 mg/sq ft of the same size distribution about 10 hr to cause 
skin burns (Fig. 15). 

Other formulations of output data can be derived from the multiparticle 
dose computations. A few examples follow. 



46 



MIKHAIL 



10 fc 



10 s 



10' 



io- 



1 1 1 


I | ! 1 ! 1 1 1 1 '_ 


- 


Deposition density, mg/sq ft" 


_ 


. 5000 


—^ — 


— 2000 — 


^ — 


^^______^_— 1 000 


^^^ 


500 


^^^^ 


200 - 


-^^^^ 


100 


: i i 


: . i ill! i ii! 



10 c 



10 1 10 : 

RETENTION TIME, hr 



10' 



Fig. 11 Dose delivered to the skin by multiparticle fallout of 100-m mean 
diameter and 1000-m maximum diameter at an exposure starting time of 10 
sec after detonation. Tissue depth, 100 u. 



10 fc 



10- 



g 10' 



10' 



10' 



10 L 



I II 


, , . , I I l_ 


— 


Deposition density, mg/sq ft 




5000 


^"^ 


?nno 




1000 




- ^ — 


_ ^r\n 




- 


?nn 




I , , 


inn 


I I ! ; i ; , I ill 



10 1 



10' 



10- 



RETENTION TIME, hr 



Fig. 12 Dose delivered to the skin by multiparticle fallout of 1000-m mean 
diameter and 2000-m maximum diameter at an exposure starting time of 10 
sec after detonation. Tissue depth, 100 /j. 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 



47 



10 s 



10^ 



S io' 



10 



10- 



-I II 


I | 1 1 1 1 | 1 IHI- 




Deposition density, mg/sq ft 




__ 5000 


1 ^ 


— __________ 2000 


— ^^^^ ^^^ 


^ — — 1 000 


~^^ \*** 


---"*" 500 _ 


y/^/ 


200 


-^01^ 


^^^ 100 


~ ^/^ ^ 


^^^"^ 


1 


I I I I I ! ! I III 



10' 



10' 



10- 



RETENTION TIME, hr 



Fig. 13 Dose delivered to the skin by multiparticle fallout of 100-ju mean 
diameter and 1000-m maximum diameter at an exposure starting time of 10 
see after detonation. Tissue depth, 100 u. 

m5 



10 4 - 



10 1 



. 




i i ill- 


— 


Deposi 


ion density, mg/sq ft - 


- 




^ ^ 5000 


- 




^^2000 


- 




^_^1000 


- yS 




^_^500 


— ^r S 




^_^^200 _ 


- yS 




, 100 


I , 


i ! i ii 


i i I , I I 



10 l 



10 1 



10' 



10^ 



RETENTION TIME, hr 



Fig. 14 Dose delivered to the skin by multiparticle fallout of 100-/i mean 
diameter and 1000-ju maximum diameter at an exposure starting time of 10 
sec after detonation. Tissue depth, 100 ju. 



48 



IKHAIL 



10 4 _ 



10' 



2 10' 



10 



m l - 



10" - 



10 l 



I 


Deposition density, mg/sq ft 


~ 


^y 5000 ~= 


- 


^^ ^2000 


- 


^^ ^S^^S 1 00 ° 


- 


^^ ^S' ^S ^^500 





y^ \s^ \s>r ^ 200 


-/O-^O 


/y^ >^ . 1 00 — 


; I I 


i I I 111! I III 



10 1 10' 

RETENTION TIME, hr 



10 : 



Fig. 15 Doses delivered to die skin by multiparticle fallout of 100-/u mean 
diameter and 1000-m maximum diameter at an exposure starting time of 10 
sec after detonation. Tissue depth, 100 \i. 



Table 2 presents one formulation, the effect of exposure-initiation time 
(delay time) on the Krebs dose received by the skin from the same fallout 
deposition density. The table presents doses delivered by two deposition 
densities, 100 and 2000 mg/sq ft, in each case over 1-, 2-, 5-, 10-, and 24-hr 
exposure periods, all following delays of 24, 48, 72, and 168 hr. Also given are 
the time periods for which fallout under these conditions would have to be 
retained before delivery of 5 70 rads takes place if the exposure starts at 24, 48. 
72, and 168 hr postdetonation. In both parts of the table, size distribution A is 
assumed. 

Another type of output formulation that may be useful (not illustrated) 
would show the skin dose accumulated in 1 hr, e.g., starting at fallout arrival or 
some later time, as a function of distance from ground zero for various weapon 
yields. The figure could be obtained by combining the dose data given here with 
the data of Clark and Cobbin, 15 for example; the latter data relate midrange 
particle size to downwind distance from ground zero for different weapon 
yields. It must be recognized that, for a given weapon yield and downwind 
distance, fallout phenomenology, as exemplified by the Clark— Cobbin approach, 
specifies uniquely not only (1) the midrange particle size but also (2) the 
ground-surface deposition density and (3) the times of fallout arrival and 



BETA-RADIATION DOSES FROM FALLOUT PARTICLES 

Table 2 

EFFECT OF EXPOSURE-INITIATION TIME ON KREBS 
DOSES DELIVERED TO THE SKIN* 



49 



Retention „ 

Exposure-initiation time 
time, 


hr 24 hr 48 hr 72 hr 


168 hr 


Fallout Deposition Density of 100 mg/sq ftt 



Doses received, rads: 



1 


18 


8 


5 


2 


2 


36 


16 


10 


4 


5 


84 


39 


24 


9 


10 


151 


73 


46 


17 


24 


291 


153 


101 


41 



Retention times required to accumulate 

5 70 rads, hr. 



76 



250 



600 



Doses received, rads. 



2400 



Fallout Deposition Density of 2000 mg/sq fti 



1 


466 


217 


120 


50 


2 


912 


423 


230 


98 


5 


2138 


998 


608 


228 


10 


3862 


1879 


1182 


445 


24 


7420 


3918 


2571 


1030 



Retention times required to accumulate 
570 rads. 



78 min 



170 min 



4 hr, 
40 min 



13 hr, 
20 min 



*Mean particle diameter of 100 u and maximum particle 
diameter of 1000 ju. 



,13 



t4 x 10 fissions/sq ft. 



.14 



$8x10 fissions/sq ft. 



cessation. The unique values of the deposition density and times of arrival and 
cessation would have to be considered in the preparation of a family of curves 
covering a range of weapon yields. Skin deposition density could be parameter- 
ized at, for example, 100 mg/sq ft, which would allow for consideration of 
fallout-particle resuspension, or simply for normalization to the correct 
skin-deposition value at each point. A carefully planned family of curves could 
thus provide a picture of those yields and downwind distances at which a 1-hr 



50 MIKHAIL 

exposure to fallout which starts to deposit on the skin at arrival time or later 
would produce the critical skin dose of 570 rads. Such kinds of results could be 
most useful in postattack planning. 

REFERENCES 

1. R. Loevinger, E. M. Japha, and G. C. Brownell, Discrete Radioisotope Sources, in 
Radiation Dosimetry, pp. 693 — 754. Academic Press, Inc., New York, 1956. 

2. J. C. Ulberg and D. B. Kochendorfer, Models for Estimating Beta Dose to Tissue from 
Particle Debris in Aerospace Nuclear Applications, USAEC Report USNRDL-TR-1 107, 
Naval Radiological Defense Laboratory, Dec. 12. 1966. 

3. O. H. Hogan, P. E. Zigman, and J. L. Mackin, Beta Spectra II. Spectra of Individual 
Negatron Emitters, Naval Radiological Defense Laboratory, USAEC Report USNRDL- 
TR-802, Dec. 16, 1964. 

4. C. F. Miller, Fallout and Radiological Countermeasures. Volume I, Report AD-410522, 
Stanford Research Institute (Project No. IM-4021), 1963. 

5. R. F. Korts and J. H. Norman, A Calculational Model for Condensed State Diffusion 
Controlled Fission Product Absorption During Fallout Formation, Report GA-7598, 
General Dynamics Corp., General Atomic Div., Jan. 10, 1967. 

6. L. V. Spencer, Energy Dissipation by Fast Electrons, National Bureau of Standards, 
Monograph 1, 1959. 

7. G. B. Curtis and J. S. Petty, A Program to Compute Beta Radiation Dosage. Volume I. 
Program Description. Final Report, USAEC Report TID-24033(Vol. 1), American 
Research Corp., Aug. 1. 1967. 

8. S. Z. Mikhail, Tissue Beta Radiation Doses from Particulate Fission-Product Sources: 
Comparison of Model Predictions with Experimental and Monte Carlo Values, Report 
ESA-TR- 70-01, Environmental Science Associates, 1970. 

9. R. Loevinger, Extrapolation Chamber for the Measurement of Beta Sources, Rev. Sci. 
Instr., 24: 907 (1953). 

10. J. S. Krebs, The Response of Mammalian Skin to Irradiation with Particles of Reactor 
Debris, Report USNRDL-TR-67-1 18, Naval Radiological Defense Laboratory, 1967. 

11. P. D. Forbes and S. Z. Mikhail, Acute Lesions in Skin Produced by Radioactive 
Microspheres, Temple University Report, Contract SNPN-49, 1970. 

12. S. L. Brown, Disintegration Rate Multipliers in Beta-Emitter Dose Calculations, USAEC 
file No. NP-15714, Stanford Research Institute (SRI Project MU-5116), August 1965. 

13. J. S. Krebs,Stanford Research Institute, personal communication, September 1970. 

14. B. R. Fish, Environmental Studies: Radiological Significance of Nuclear Rocket Debris. 
Semiannual Progress Report July 1-Dec. 31, 1964, USAEC Report ORNL-TM-1053, 
Oak Ridge National Laboratory, April 1965. (Classified) 

15. D. E. Clark. Jr., and W. C. Cobbin, Some Relationships Among Particle Size, Mass Level 
and Radiation Intensitv of Fallout from a Land-Surface Nuclear Detonation, Report 
USNRDL-TR-639, Naval Radiological Defense Laboratory, Mar. 21, 1963. 



MEASUREMENT AND COMPUTATIONAL 
TECHNIQUES IN BETA DOSIMETRY 



JAMES MACKIN, STEPHEN BROWN, and WILLIAM LANE 

Stanford Research Institute, Menlo Park, California 



ABSTRACT 

A small beta dosimeter developed for use in biological-effects experiments was calibrated 
and tested in a series of laboratory experiments, including a uniform-volume-source 
exposure, a point-source exposure, surface-roughness exposures, and an environmental 
resistance test. The dosimeters were then used in cooperation with biological experiments 
being conducted by other investigators. These included a plant-community exposure, a 
corn-plot exposure, three wheat and potato exposures, and a field test of surface roughness. 
The measured data were then compared with calculated values, and, in general, agreement 
was found to be satisfactory. 



The beta-ray component of fallout radiation is important to many biological and 
ecological effects of nuclear war. For some small organisms, including most food 
and feed-crop plants, it is surely the dominant component, at least in the early 
stages of growth. Recognizing the importance of estimating biological damage 
from beta radiation, Stanford Research Institute (SRI) conducted a series of 
theoretical and experimental studies in an attempt to make such estimates with 
accuracies sufficient for damage-assessment studies. 1 5 

When young bean plants were exposed to 90 Y radiation, 2 both contact- 
source and beta-bath geometries produced plant sterility at estimated doses of 
100,000 rads to leaves and 2000 rads to meristems. Although these few results 
only indicated a range of expected results, they verified the need for additional 
studies of beta-dose computation and measurement. 

The theoretical basis for the interpretation of beta dose was investigated by 
comparing the results of computational models 3 ' 4 with experimental measure- 
ments made with lithium fluoride powder exposed to a variety of 90 Y sources. 5 
In the simplest geometries the comparison was quite good, but the computa- 
tional procedures were not sufficiently developed to deal accurately with some 

51 



52 MACKIN, BROWN, AND LANE 

of the more complicated cases. In a damage-assessment context, however, the 
discrepancies were not large enough to make damage estimates grossly uncertain. 
In such a context, then, the agreement for the relatively simple geometries was 
adequate. Real fallout exposures are not even relatively simple, however; they 
deal with very complex geometries that would require an inordinate effort to 
model mathematically. Methods must be sought that can estimate beta damage 
with much less effort. 



APPROACH 

The specific objective of our investigation was to develop better dosimetric 
methods for use in biological-effects experiments and thus to provide a means 
for relating observed effects to existing and revised computational methods. To 
this end, a small beta dosimeter was developed and tested in the laboratory and 
then was used to measure beta doses in field experiments conducted by 
cooperating investigators. 

Preparation of Sources 

In all cases the basic starting material for the preparation of each radiation 
source was an essentially carrier-free solution of 90 Y activity. Aliquots were 
taken from each solution to prepare sources in the form of (1) activity 
uniformly dispersed in gelatin, (2) evaporated aliquots of solution, and (3) 
synthetic fallout. The gelatin sources were prepared simply by adding measured 
amounts of active solution to stirred suspensions of gelatin in distilled water and 
pouring the gelatin into suitable molds for hardening. 

Sources prepared from liquid aliquots were made by stretching Mylar film 
over a given substrate, usually a clear plastic. A small aliquot was handpipetted 
onto the film and then air dried. The sources were stripped from the substrate 
after exposures were completed and were measured directly in the ionization 
chamber. 

The basic material employed for the preparation of solid sources was 
synthetic fallout of particles in the sieve size range of 88 to 177 fl. The fallout 
simulant was prepared by spraying an aliquot of radionuclide solution on a sized 
portion of warm sand, heating it slowly to dryness, and then thermally treating 
it at high temperaaire so that the activity is fixed on the particle surfaces. Solid 
sources for surface-roughness experiments were prepared by dispersing the 
simulant in air and permitting the particles to fall under gravity. A cylindrical 
pipe 3 ft long and 6 in. in diameter, positioned over the substrate, was used to 
direct the particles uniformlv over a circular area. 

In the field experiments the method of fallout-simulant dispersal was 
determined by the cooperating investigator. The University of North Carolina 
experiments used a shielded container from which the simulant was dispersed 
through a slit. The container was moved over the plots by hand. In the 



MEASUREMENT AND COMPUTATIONAL TECHNIQUES 53 

University of California experiments, the method of dispersal utilized a 
motorized hopper that reciprocated across the plot while being moved down the 
plot on railings. Dispersal was accomplished by a rotary rod that fed simulant 
into a long slot as in a lawn seeder. 

Radiation Dosimetry 

A principal objective of the research was to develop a dosimetric method 
that was more convenient than the loose-powder method used in the previous 
work. The loose-powder method used thermoluminescent lithium fluoride (LiF) 
powder, which has a wide range of dose sensitivities (from a few millirads to 
kilorads), low energy dependence, reproducibility, and stability. A disadvantage 
of the loose-powder method is that much care must be exercised both in 
emplacement and in subsequent recover) 7 of the material. 

To surmount this difficulty, we mounted a joint effort with Radiation 
Detection Co. to design a convenient dosimeter with the features mentioned 
previously. The dosimetric material was again LiF powder,* in the size range 80 
to 200 mesh, which was obtained in quantity and standardized with 60 Co. 
Calibration of each dosimeter independently was unnecessary. This simplified 
the experimental procedures since the dosimeters were completely inter- 
changeable. Calibration was based on exposure of aliquots of powder to Co 
and on the factor 0.807 rad/R. The factor was based on 0.869 rad deposited in 
air per roentgen and 0.929 for the ratio of stopping powers for 60 Co gammas for 
LiF and air. 

The LiF powder was encapsulated in glass capillary tubing approximately 
2 mm in outside diameter and about 0.1 mm (31.8 mg/cm 2 ) thick and was 
sealed by flaming. The dosimeters, which averaged about 5 mm long and 
contained either 6 or 12 mg of LiF powder each, were individually tested for 
environmental closure by being allowed to stand under 30 cm of water for 
15 min or longer. When returned to Radiation Detection Co. for readout, they 
were placed in a special planchet, and the luminescence was measured directly 
through the glass in a Mark IV model 1 100 TLD Reader. 

Method of Comparison 

Theory and experiment were compared in terms of the disintegration-rate 
multiplier (DRM). The DRM for experimental results is obtained by dividing the 
observed dose by the total number of disintegrations during the period of 
exposure: 






DRM = -f-(- — ^ — I (1) 



*The powder used was Radiation Detection Co. "Throwaway" Powder, Batch 8/69, 
having linear response to gamma radiation through 10,000 rads. 



54 MACKIN, BROWN, AND LANE 

where D = dose, rads 

B = initial source strength, dis/sec/unit area, volume, or mass, as ap- 
propriate 
A = decay constant for 90 Y (3.0 X 10" 6 /sec) 
t = exposure time, sec 

Infinite-medium methods, line-of-flight perturbation methods, or pseudo- 
source methods were used in the computation of beta dose. These models are 
described in another report 5 and will not be discussed here. In judging the 
adequacy of the comparisons, we developed the rule of thumb that agreement 
with a factor of 2, on the average, was acceptable. This degree of uncertaintv has 
been shown to result in less than 10% uncertainty in damage-assessment results. 



Results of Experiments 

Several laboratory experiments were conducted to test the dosimeter. First, 
dosimeters were calibrated by exposure to an effectively infinite uniform-volume 
source. Next, verification of their performance was obtained with exposures at 
various distances from a point source. The geometrical backscattering effect 
previously reported was again observed. A series of exposures using a 
fallout-simulant source distributed on sized pebble substrates was then per- 
formed. The general features of the measured surface-roughness attenuation 
factor were similar to those found before, but the variation in the factor with 
substrate particle size was less pronounced than previously, probably because of 
differences in handling between dispersal and exposure. 

Several sets of field-exposure measurements were also conducted. Two plant 
communities were contaminated with fallout simulant by investigators from the 
University of North Carolina, and dose measurements were made with SRI 
dosimeters. The comparison of measured and calculated doses was satisfactory 
within the uncertainties of the exposure geometry. Next, a plot of corn plants 
was contaminated with fallout simulant by investigators from the University of 
California, Berkeley, and again dosimeters were distributed on and near the 
plants. Agreement was not so good as previously, because of difficulties in 
dispersing the simulant and recovering the dosimeters, but order-of-magnitude 
agreement was obtained. In a second University of California series plots 
containing wheat and potato plants were contaminated. Agreement between 
measured and calculated values was again found to be good, except where the 
computational model was clearly inappropriate. The final set of dose measure- 
ments, taken over a smooth plot of contaminated loam, yielded a surface- 
roughness factor of about 0.75. 

Reasonable agreement between calculated and observed beta doses can 
therefore be obtained when sufficiently good input information can be provided 
for the computations. More effort is indicated to obtain better input values for 
such parameters as plant density and fraction of fallout retained on foliage. 



MEASUREMENT AND COMPUTATIONAL TECHNIQUES 55 

Attention should also be given to empirical dose-prediction methods that do not 
depend so heavily on precise input information. 



REFERENCES 

1. S. L. Brown, Disintegration Rate Multipliers in Beta-Emitter Dose Calculations, USAEC 
file No. NP-15 714, Stanford Research Institute (SRI Project No. MU-5116), August 
1965. 

2. W. B. Lane and J. L. Mackin, Response of Bean Plants to Beta Dose Problems, Report 
TRC-68-16, Stanford Research Institute, November 1967. 

3. S. L. Brown and O. S. Yu, Computational Techniques in Beta Dose Problems, Report 
TRC-68-13, Stanford Research Institute, January 1968. 

4. S. L. Brown, Beta Radiation Effects on Agriculture, Report TN-RMR-34, Stanford 
Research Institute, June 1968. 

5. J. L. Mackin, S. L. Brown, and W. B. Lane, Beta Radiation Dosimetry for Fallout 
Exposure Estimates: Comparison of Theory and Experiment, Report TRC-69-26, 
Stanford Research Institute, June 1969. 

6. S. L. Brown, W. B. Lane, and J. L. Mackin, Beta Radiation Hazard Evaluation, Stanford 
Research Institute, (in press). 



MEASUREMENT OF BETA DOSE 

TO VEGETATION FROM CLOSE-IN FALLOUT 



A. D. KANTZ 

EG&G, Inc., Santa Barbara Division. Goleta, California 



ABSTRACT 

Dosimetry experiments are described in which both beta and gamma-ray doses to the 
environment and to vegetation were measured with thermoluminescent dosimetric tech- 
niques in the close-in fallout fields from the Plowshare cratering events Cabriolet and 
Schooner. The beta doses measured were found to be an order of magnitude greater than 
the gamma-ray doses at the same locations. This work was performed in support of 
ecological- and environmental-effects studies sponsored by the Environmental Sciences 
Branch of the Atomic Energy Commission's Division of Biology and Medicine. 



Before the Plowshare Palanquin event in April 1965, radiation damage to 
vegetation from nuclear detonations, whether aboveground or belowground, was 
attributed largely to heat, blast, and thermal shock. 1 After the Palanquin 
detonation, however, extensive damage to vegetation was observed over an area 
of about 4 km 2 in which there was no evidence of blast, shock, or thermal 
damage except in the immediate vicinity of the crater. 1 ° 

Since an experimental study of the gamma-ray doses required to kill the 
various tvpes of vegetation prevalent at the Palanquin site revealed that the 
amount of radiation encountered on the peripheries of the damage patterns was 
insufficient to account for the observed damage, it was hypothesized that beta 
radiation was a contributing factor. To validate this view, we developed special 
dosimetry techniques for measuring the gamma-ray and beta dose in the fallout 
fields of subsequent Plowshare cratering events. The objectives were to: 

1. Determine the total dose to plants and distinguish clearly between 
gamma-ray and electron contributions. 

2. Evaluate any low-energy photon contribution. 

3. Specify as much information as possible regarding the energy and 
distribution of the beta sources. 

56 



MEASUREMENT OF BETA DOSE TO VEGETATION 57 

This paper describes the dosimetry techniques and their application to 
radiation-dose measurements in support of ecological- and environmental-effects 
studies sponsored by the Environmental Sciences Branch of the Atomic Energy 
Commission's Division of Biology and Medicine during the Cabriolet and 
Schooner cratering events at the Nevada Test Site in 1968. The assessment of 
vegetation damage is described in studies by Rhoads et al. 1 l A 2 

DOSIMETRY TECHNIQUES 

The general characteristics of fallout radiation expected from a cratering 
event include a 1-MeV gamma-ray component, an associated beta component 
with energies in the 1-MeV region, and a possible low-energy-photon character- 
istic. Two approaches for measuring this mixed field are equally valid: (1) 
measurement of fluence and interpretation of dose deposition or (2) direct 
measurement of absorbed dose in some material and correlation with another 
material through known absorption coefficients. 

Because of time constraints and the need for obtaining the best information 
possible on the beta source, we chose the more straightforward of the two 
methods, that of measuring fluence by determination of depth-dose profiles, for 
the Cabriolet and Schooner events. 

Dosimeter Design 

The dosimeters for these experiments had to be designed to accommodate 
very wide dose ranges and to be capable of withstanding weathering under severe 
winter conditions at an elevation of 6000 ft for a period of several weeks. Also, 
because of the large number of dosimeters required, logistical considerations 
made it desirable for the dosimeters to be easy to fabricate, field, and analyze. 
Calcium fluoride (CaF 2 ) appeared to fulfill these requirements, and ther- 
moluminescent dosimeters (TLD's) made up of hot-pressed chips of CaF 2 — Mn 
measuring 3 by 3 by 1.5 mm were constructed. 

The dosimeters, which were designed to simulate energy deposition from 
ionizing radiation in plant tissue, consisted of a 32-mm-square piece of 
3-mm-thick plastic polycarbonate containing eight holes, each 7 mm in diameter 
(see Fig. 1). The CaF 2 — Mn chips, with individual shields, were placed in the 
holes, and the entire dosimeter was covered by a thin, light-tight film. The 
shielding for the chips during the Cabriolet event was as follows: (1) none except 
the thin, light-tight covering, (2) 0.17-mm Mylar, (3) 0.55-mm polycarbonate, 
(4) 1.55-mm polycarbonate, (5) 0.85-mm aluminum, and (6) 0.5-mm lead. 

Since the thickness of the TLD chips was sufficient to completely stop 
electrons with energies up to 1.0 MeV, readings on individual chips were 
proportional to energy fluence incident on the chip. The change in fluence (ergs 
per square centimeter) as mass was added in front of the TLD was used to infer 
the dose (ergs per gram). 



58 



KANTZ 




Fig. 1 Thermoluminescent dosimeters (TLD's) constructed for the Cabriolet 
event. Shown from left to right are the open TLD holders, the holders with 
chips in place, and the dosimeters ready for use in the field. 



Shielding was selected to produce a gradual decrease in beta contribution, 
the thickest shield being capable of stopping the most energetic beta particles. 
This thickness, however, did not require significant correction for the absorption 
of 1-MeV gamma rays. The presence of a low-energy-photon component could 
be inferred by differences in the stopping power of polycarbonate and 
aluminum. These materials present equal absorption of electrons but have a Z 
dependence for absorption of low-energy photons. Thus a high reading for the 
polycarbonate-shielded chips signified a low-energy-photon component whose 
magnitude could be estimated. 



Field Arrangement 

For the Cabriolet event the dosimetry stations were positioned along two 
arcs (Fig. 2). This arrangement was based on records of the early dose rates for 
the preceding Palanquin event and on the availability of materials and personnel. 
The first arc was along a radius 610 m (2000 ft) from ground zero (GZ), 
extending from 3 30° on the west to 90° on the east. The second arc, which was 
along a radius 915 m (3000 ft) from GZ, was much shorter than the first and 
covered the direction from GZ considered most likely to be contaminated on the 
basis of weather conditions anticipated at the time of the event. 



MEASUREMENT OF BETA DOSE TO VEGETATION 



59 




SCALE IN FEET 



500 I0O0 



SCALE IN METERS 



100 200 300 



Fig. 2 Map of the Cabriolet area, showing locations of arcs along which 
dosimetry stations were positioned. 



At each station along the arcs, the dosimeters were suspended from a vertical 
wire and were arranged in an array so that each dosimeter lay in a horizontal 
plane. The dosimeters were spaced above the soil surface at various distances to 
take advantage of the beta shielding represented by the air path from the ground 
to the dosimeter. The highest dosimeter was 150 cm above the soil surface; this 
was expected to be sufficient to raise it out of the beta bath. 



60 KANTZ 

Plant Correlation 

Additional smaller dosimeters with only three chips were prepared and 
placed directly on shrubs in the vicinity of the vertical arrays. It was expected 
that the readings from the dosimeter 25 cm above the soil surface in the vertical 
array would closely resemble the average absorbed dose in the surrounding 
shrubs. The smaller dosimeters were fabricated with the following shielding: (1) 
minimum shielding, afforded by the thin cover, (2) a thick cover of lead capable 
of completely stopping the electrons so that no beta dose could be received, and 
(3) an intermediate shielding representing the gamma-ray background and a 
fraction of the beta contribution. 

The dosimeters were arranged carefully ' on the exterior of shrubs in the 
immediate vicinity of the vertical stations and were oriented so that one 
dosimeter was on the front of the shrub (toward GZ), one on the back, one on 
the top, and one at a third side. 

To further delineate the radiation levels, we fabricated a plant phantom for 
use as a fallout collector for each vertical array. The phantom consisted of two 
wire-mesh cylinders, one placed inside the other, with opposite ends closed. The 
cylinders were covered with cheesecloth, which had previously proved to be an 
efficient collector of radioactive debris. The retentive capacity of the phantoms 
for fallout was expected to be similar to that of actual shrubs. Dosimeters were 
placed on the shrub phantoms to correlate with the vertical arrays. These 
dosimeters successfully measured the small differences in both gamma-ray 
background and beta dose in the various geometries described. 

Dosimeter Readout and Analysis 

The dosimeter packages from the field were individually read out in a 
standard EG&G model TL-3 reader. Since the chips were calibrated against a 
standard 60 Co source, the scale readings were a direct measure of the exposure 
in roentgens. 

The energy deposited in a CaF 2 — Mn chip when it is exposed to a calibrating 
Co source is 

Ej = 86R(pAt) ergs (1) 

where R = exposure in roentgens 

p = density of the dosimeter 
A = area of the dosimeter 
t = thickness of the dosimeter 

The light emitted when the dosimeter is read is proportional to the energy (Ej ): 

L^cEi (2) 



MEASUREMENT OF BETA DOSE TO VEGETATION 61 

When the dosimeter is exposed to low-energy beta radiation and subsequently 
read out, the energy deposited per unit area is 

E 2 L 2 L 2 86RpAt 2 

0= a=7a = X-T7~ ergs/cm (3) 

If the readout instrument is adjusted to read in roentgens (R — L x ), the final 
calibrating formula is 

= 86pt X L 2 ergs/cm 2 (4) 

For a typical chip pt is 0.550 g/cm 2 . The calibrating relation is then 

= 47.3L 2 ergs/cm 2 (5) 

where L 2 is the scale reading on the dosimeter. 

Dose may be inferred from the readings (pi and 2 on two dosimeters 
covered by absorbers having masses mi and m 2 : 



D = J ^_^ (6) 

m t — m 2 

In this case dose is determined for the absorbing material. 

Data taken with the use of Mylar may be used to infer dose in water by 
multiplying by the stopping power for water and dividing by the stopping power 
for Mylar: 

(dE/dx) H2 o 

D H 2 ~ D Mylar X . ,„. , : (7) 

(dE/dx) Mylar 



RESULTS AND DISCUSSION 
Project Cabriolet Dosimetry 

The data from each array were plotted as a function of shield thickness. 
Station 7, near the center of the fallout pattern, shows the typical decrease in 
scale readings with increasing shield thickness (Fig. 3). The residual reading 
(from the lead-covered chip) was due to gamma-ray radiation. For every station 
the gamma-ray contribution was found to be the same for each vertical position, 
within a probable error of ±3%. 

The contribution of the gamma-ray dose was subtracted and the beta 
contribution evaluated from plots for each of the stations recovered. The 
penetration by the beta source through the shielding indicated an average range 



t 



62 



KANTZ 



of about 325 mg/cm 2 of Mylar. This corresponds to a beta source having a 
maximum energy of approximately 850 keV. 

The maximum gamma-ray dose encountered on the Cabriolet event in the 
center of the fallout pattern was approximately 700 rads (absorbed dose in 
water). Figure 4 shows the variation seen in the gamma-ray dose from the 
vertical array, from shrubs in the immediate vicinity of the stations, and on 
simulation shrub phantoms. 



300 



200 - 



100 - 




~° °~, 25 cm off ground 

~o o-, 150 cm off ground 

-A- — •£-, Ground level 



100 



200 300 400 

DEPTH, mg/cm 2 OF MYLAR 



500 



Fig. 3 Depth dose at Station 7 (Cabriolet). 



Figure 5 illustrates the gamma-ray radiation doses experienced by Artemisia 
shrubs in the vicinity of the stations and the variations in the doses received by 
the fronts, tops, and backs of the shrubs. It is evident from the illustrated data 
that the fronts received the greatest gamma-ray dose; the backs were protected 
to some extent. As anticipated, the variations in the doses were greatest in the 
center of the fallout pattern where erratic distribution could be expected. 

The beta doses shown in Fig. 6 are derived for the dose that would be 
absorbed on the surface of vegetation located at that point. The pattern of the 
variations seen is somewhat different from the gamma-ray distribution. The beta 
doses tend to increase in the lower topographical regions where the gamma-ray 
contributions decreased. The protection of the backs of the shrubs is very 
marked in the center of the fallout pattern. The dependence is shown in Fig. 7. 
In regions outside the central pattern, the differences between front and back 
are negligible. 



MEASUREMENT OF BETA DOSE TO VEGETATION 



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MEASUREMENT OF BETA DOSE TO VEGETATION 



67 



Project Schooner 

The area of ecological interest in the Schooner cratering event was a valley 
protected from the direct line of sight from GZ by canyon walls. The dosimetry 
instrumentation and techniques used to measure doses to the environment and 
vegetation were patterned closely after those used in the Cabriolet event. 
However, certain modifications and additions were incorporated based on the 
Cabriolet results. 

The beta penetration to 325 mg/cm 2 of tissue during Cabriolet indicated 
that dosimeters should be placed 3 to 4 m aboveground to escape the beta bath. 
Therefore during the Schooner event dosimeters were positioned at distances of 
25, 100, and 300 cm above the soil surface in vertical arrays. Figure 8 shows the 
results of measurements at Station near the edge of the central fallout pattern. 
The depth-dose profile obtained was very similar to that measured at Cabriolet, 
and the beta penetration was identical. 



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100 



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DEPTH, mg/cm 2 



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Fig. 8 Depth dose at Station (Schooner). 



For the Schooner event two of the eight CaF 2 — Mn chips in the dosimeters 
were provided with shielding only on the upper side or only on the lower side. 
Thus a beta source exclusively limited to the ground could be expected to 
contribute to the dose measured on one of the chips and a source from the sky 
to contribute exclusively to the other. The results of this directional lead 



68 



KANTZ 




Beta-dose source 
Lead-covered chips 25 cm 

— ^>— , Total beta dose 

O""", Lead covers open up 

— WW— t Lead covers open down 



20N 



10N 



10 20 

STATION NO. 



30 



40 



Fig. 9 Distribution of beta source in the Schooner event. 



shielding presented interesting information for the interpretation of the beta 
source. The beta distribution data in Fig. 9 show that in the major fallout 
pattern (centered at Station 7N) the TLD chips with lead covers open toward 
the ground experienced three times the beta dose of those open toward the sky. 
In a secondary peak near Station 3 3, the contributions are essentially equal; the 
chips exposed to the sky show a slight additional beta dose compared to those 
open toward the ground. 



MEASUREMENT OF BETA DOSE TO VEGETATION 69 

The marked differences in the absorbed dose observed at Cabriolet in the 
fronts, tops, and backs of shrubs were not detected. Instead, dosimeters placed 
at these positions received the same dose within the statistics of the 
measurements. Also, the type of vegetation damage observed after this event 
contrasted sharply with that observed at Cabriolet. 

The effects of close-in fallout on vegetation at the Schooner site are 
described in detail by Rhoads et al. 1 2 in this volume. 

Direct Dose Measurements for Future Events 

To supplement the method of determining the energy fluence and the 
interpretation in terms of absorbed dose, we can use a dosimeter material 
directly to measure absorbed dose if it absorbs only a negligible portion of the 
incident radiation (i.e., if, considering an absorption of the form E e Mt , the 
material is "thin" under the condition that^t ^ 0). 

From the experience gained in measuring depth dose in cratering fallout 
fields, we determined that a direct-reading dosimeter having a small thickness 
compared with the beta range of 325 mg/cm could be made. This dosimeter, 
which consists of a 0.012-in. cube of hot-pressed CaF 2 — Mn, was found to have a 
stable geometry, and measurements made with it in radiation fields were 
consistent within a probable error of ±3 R. 

This small cube can be placed directly alongside a stem, leaf, or branch or at 
a meristem; thus dosimetric measurements can be made at the vital points of 
interest to ecological studies. The gamma-ray contributions can be evaluated in a 
manner similar to that of the fluence measurements by shielding with sufficient 
material to absorb electrons entirely while producing a negligible effect on the 
gamma-ray component. 

In summary, the direct measurement of absorbed dose by the small, 12-mil 
cubes of CaFS - Mn greatly simplifies the logistics of making dosimetry 
measurements on cratering events. Such dosimeters have been fabricated for use 
in ecological and environmental studies of fallout effects during any future 
events. 



ACKNOWLEDGMENT 

This work was done under Contract No. AT(29-1)-1 183 between Environ- 
mental Sciences Branch, Division of Biology and Medicine, U. S. Atomic Energy 
Commission, and EG&G, Inc., Santa Barbara Division. 

REFERENCES 

1. Roy Overstreet et al., Preliminary Report, Trinity Survey Program, August 1947, 
USAEC Report, University of California, Los Angeles, 1947. 



70 KANTZ 

2. S. L. Warren and A. W. Bellamay (Comps.), The 1948 Radiological and Biological 
Survey of Areas in New Mexico Affected by the First Atomic Bomb Detonation, 
USAEC Report UCLA-32, University of California, Los Angeles, Oct. 12, 1949. 

3. K. H. Larson et al., Alpha Activity Due to the 1945 Atomic Bomb Detonation at 
Trinity, Alamogordo, New Mexico, USAEC Report UCLA-108, University of California, 
Los Angeles, Jan. 5, 1951. 

4. J. L. Leitch, Summary of the Radiological Finding in Animals from the Biological 
Surveys 1947, 1948, 1949, and 1950, USAEC Report UCLA-Ill, University of 
California, Los Angeles, Feb. 7, 1951. 

5. K. H. Larson, J. H. Olafson, J. W. Neel, W. F. Dunn, S. H. Gordon, and B. Gillooly, The 
1949 and 1950 Radiological Soil Survey of Fission Product Contamination and Some 
Soil-Plant Interrelationships of Areas in New Mexico Affected by the First Atomic 
Bomb Detonation, USAEC Report UCLA-140, University of California, Los Angeles, 
May 31, 1951. 

6. Lora M. Shields and P. V. Wells, Effects of Nuclear Testing on Desert Vegetation, 
Science, 22: 38-40(1962). 

7. W. H. Rickard and L. M. Shields, An Early Stage in the Plant Recolonization of a 
Nuclear Target Area, Radiat. Bot., 3: 41-44 (1963). 

8. W. E. Martin, Close-in Effects of Nuclear Excavation and Radiation on Desert 
Vegetation, abstract in Radiation Effects on Natural Populations, a Colloquium Held in 
Philadelphia, May 23, 1965, George A. Sacher (Ed.), USAEC file No. NP-16374, 
pp. 7—9, Argonne National Laboratory, January 1966. 

9. Janice C. Beatley, Effects of Radioactive and Non-Radioactive Dust upon Larrea 
divaricata Cav., Nevada Test Site, Health Phys., 11: 1621-1625 (1965). 

10. W. A. Rhoads, Robert B. Piatt, and Robert A. Harvey, Radiosensitivity of Certain 
Perennial Shrub Species Based on a Study of the Nuclear Excavation Experiment, 
Palanquin, with Other Observations of Effects on the Vegetation, USAEC Report 
CEX-68.4, EG&G, Inc., May 1969. 

11. W. A. Rhoads, R. B. Piatt, R. A. Harvey, and E. M. Romney, Ecological and 
Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and 
Short-Term Effects on the Vegetation from Close-in Fallout, USAEC Report PNE-956, 
EG&G, Inc., June 25, 1969. 

12. W. A. Rhoads, H. L. Ragsdale, and R. B. Piatt, Radiation Doses to Vegetation from 
Close-in Fallout at Project Schooner, this volume. 



THE IMPORTANCE OF TRITIUM 
IN THE CIVIL-DEFENSE CONTEXT 



J. R. MARTIN and J. J. KORANDA 

Lawrence Radiation Laboratory, Bio-Medical Division, University of California, 

Livermore, California 



ABSTRACT 

The importance of tritium in the civil-defense context is assessed by comparing the dose rate 
and the 30-year dose integral for tritium from fusion with the external dose of 
gamma -emitting fission products. 

The tritium dose is computed by assuming equilibration of fallout tritium with water in 
the biosphere and with the body water of man. The fission-product gamma dose for 
late-time dose-significant nuclides is tabulated in roentgens per hour per kiloton per square 
mile as a function of time. 

Tritium is shown to be relatively unimportant in the civil-defense context when 
compared with the external gamma dose from an equal yield of fission products. 



The survival of man in an environment contaminated with radioactive fallout 
after a nuclear attack is the basis on which the importance of tritium in the 
civil-defense context can be assessed. Although tritium is a weak beta emitter, 
the radiation hazard to man can be significant because of the high yield of 
residual tritium from fusion devices. Also, tritium is relatively mobile and, as 
tritiated water, becomes rapidly dispersed in the environment where it is 
available for ingestion by man. On the other hand, the hazard is reduced 
somewhat by the dilution of tritium with the large amount of water in the 
environment. 

The importance of any single isotope can only be compared with respect to 
other radioisotopes produced in a nuclear explosion. As a first estimate, 
therefore, the radiation hazard to man from residual tritium is compared with 
that from fission-product radioactivity. 

When certain reasonable assumptions are made, the dose rate as a function of 
time and the 30-year dose integral can be determined per unit area and unit 

71 



72 MARTIN AND KORANDA 

explosive yield for residual tritium from fusion and for fission-product 
radioisotopes. For example, in the civil-defense context we assume a 2-week 
shelter period following the detonation of nuclear weapons with equal parts of 
fission and fusion. The 2-week shelter period eliminates blast, heat, shock-wave, 
and prompt-radiation effects from consideration. The assumption of equal parts 
of fission and fusion is necessary to normalize the explosive yield. The results 
obtained in this study can be scaled directly for any other ratio of fission to 
fusion. 

Finally, we assume that fallout is uniformly deposited over an area of 1 sq 
mile per kiloton of yield. The essential consideration of this assumption is that 
tritium is distributed in the same manner as the fission products are. Any 
deviation from uniform distribution will not affect the results of this study as 
long as the distribution of tritium and of fission-product fallout changes in the 
same way. The results can also be scaled directly for any area of deposition per 
unit explosive yield. 

Fleming 1 provides a convenient summary of external gamma dose as a 
function of time for uniformly deposited, unfractionated plutonium fission 
products in roentgens per hour per kiloton per square mile. To simplify, we will 
consider in comparison with the tritium dose only the nuclides that contribute 
significantly to the external gamma dose at late times. Many short-lived fission 
products are, of course, eliminated from consideration by the 2-week shelter 
period. 

The tritium dose rate can be expressed in the same terms as the gamma dose 
rate if we assume that the uniformly distributed residual tritium yield is 
thoroughly mixed and in equilibrium with water in the fallout environment by 
the end of the 2-week shelter period. The specific-activity approach then permits 
dose calculations based on equilibration of tritiated w^ater with vegetation, 
livestock, and man. 

TRITIUM DOSIMETRY 

To use the specific-activity approach, we must determine the water 
compartment of the biosphere in which tritium fallout will be mixed. The water 
compartment can be estimated from studies of the behavior of tritium in a 
desert ecosystem by Koranda and Martin" and in the tropical rain-forest 
ecosystem by Martin et al. 3 and Jordan et al. 4 These studies show T that tritium 
behavior in the environment is influenced largely by rainfall. These diverse 
ecosystems probably represent the extremes of the range of rainfall, from the 
low of 5 in. /year in the desert to the high of 100 in. /year in the rain forest. 

Tritium behavior can be considered in terms of a simple mixed-tank model. 
A single deposition of tritium is assumed to mix completely with a finite 
soil— water volume defined as the water-compartment capacity, C. The incoming 
flux of rainwater, F, which represents the flow through the compartment, is 



IMPORTANCE OF TRITIUM 73 

assumed to be immediately and completely mixed with the water compartment. 
The outgoing flux of water from the compartment, which must be equal to the 
incoming flux, contains the instantaneously diluted concentration of tritium. 
Thus the physical removal of tritium is exponential with time. The mean 
residence time for tritium, T, defined as the average time a tritium atom remains 
in the compartment, is given by the ratio of the capacity, C, to the flux, F: 

T = § (1) 

F 

The exponential physical removal of tritium was demonstrated in the desert 
and rain-forest ecosystem studies. The capacity of the water compartment, C, 
can be determined from a measurement of the flux of rainwater, F. and the 
observed mean residence time, T: 

C=FT (2) 

In the rain-forest experiment described by Jordan et al., 4 the surface deposit 
of tritium moved down into the soil profile, giving a peaked distribution with 
depth. The peak tritium concentration moved deeper into the soil profile and 
became more diffuse with time. Martin et al. 3 described how the residence time 
was determined by plotting the integrals of the tritium depth-distribution curves 
with time. The mean residence time for tritium in the rain-forest ecosystem 
following a surface application was 42 days. The incoming flux of rain was 
100 in. /year, or 6.66 kg/m 2 /day; thus, from Eq. 2, the capacity of the water 
compartment is 

C = FT = 6.66 X 42 = 280 kg/m 2 (2a) 

A similar pattern of tritium behavior with time was observed in the soil of 
the desert ecosystem at the Sedan crater. The mean residence time for tritium 
determined by Martin and Koranda 5 was 18.8 months, or 570 days. The 
incoming flux of rain was only 5 in. /year, or 0.3 5 kg/m 2 /day; thus the 
water-compartment capacity is 

C = FT = 0.35 X 570 = 200 kg/m 2 (2b) 

The agreement in the calculated values for the water-compartment capacity 
of these diverse ecosystems can be explained by the difference in the depth of 
the zone of interaction of their respective soils. Although the rain-forest soil had 
a relatively high average water content, only a shallow layer of soil water mixed 
with incoming rain. The water compartment of the wet tropical rain-forest soil 
corresponded to a depth zone of less than 2 ft. In the dry desert soils, significant 
interaction of tritium was observed at depths of 6 ft. The estimated water- 



74 MARTIN AND KORANDA 

compartment capacity for the biosphere was therefore taken to be the average 
value, 240 kg/m 2 . 

This estimate is conservatively low with respect to dose calculations because 
desert plants growing at the Sedan crater typically had tritium concentrations in 
their water; this indicated a water compartment of three to nine times that of 
the measured value. There appeared to be greater dilution of the tritium than 
could be accounted for by the water compartment. This is apparently due to the 
fact that the tritium is not uniformly distributed in the soil. The plants draw 
water from selected depths in the soil, whereas the water compartment is 
determined from the integrated depth profile. 

The tritium concentration in the biosphere can be calculated from a tritium 
yield of 2 g/kt dispersed over a 1 sq mile area and diluted by the water 
compartment of 240 kg/m" . The resulting specific activity of tritium, A, is 

_ (2 g/kt)(9800 Ci/g) (3.86 X 10" 7 sq mile/m 2 ) 
240 kg/m 2 

= 3.15 X 10 5 Ci/kg/kt/sq mile 

If a man is equilibrated with this specific activity, the resulting dose rate, D , 
is 

D = (3.15 X 10" 5 Ci/kg/kt/sq mile) (7.44 R/hr/Ci/kg) 

(4) 
= 2.34 X 10" 4 R/hr/kt/sq mile 

The dose rate, D t , at any time, t, is 

D t = D e" a P + X r k (5) 

where X r is the radiological decay constant for tritium (0.0565 year l ) and X p is 
the physical-removal decay constant. 

The integrated dose, I, from t = to t = t, is given by 

T D [l-e^P + V*] 

* t = > > (6) 

The 30-year dose integral for no physical removal (A = 0) is 

i3 O= 2 - 34X l°" 4 (87 60hr/vear)[l-e- 3O(O - 0565) ] R/kt/sq mile (7) 
0.0565 

I 30 = 30 R/kt/sq mile (7a) 

If allowance is made for the physical residence time of tritium, the 30-year 
dose integral is much lower. Even when the most conservative observed value, 



IMPORTANCE OF TRITIUM 75 

18.8 months (A = 0.639 year ' ), in the desert ecosystem is used for the physical 
residence time, the dose integral becomes 

I 30 ' = 3 R/kt/sq mile (7b) 



FISSION-PRODUCT DOSIMETRY 

The dose rate at various times and the 2-week to 30-year dose integral for 
the late-time dose-significant gamma-emitting fission products are given in 
Table 1. The dose rates were taken directly from Fleming's data, 1 in which the 
point of exposure is 3 ft above a smooth infinite plane uniformly contaminated 
with the nuclide in question. The late-time dose-significant nuclides are those 
which contribute 1% or more of the total external gamma dose integral from 
2 weeks to 30 years. The nuclides listed account for more than 95% of the dose 
rate at any time after 2 weeks postdetonation. 

At early times after the 2-week shelter period, the dose rate is due mainly to 
fission products with half-lives in the range of several days to several weeks. The 
contribution of 1 40 Ba— * 40 La, for example, is half the total dose rate at 
t = 2 weeks. The contribution of these nuclides falls off rapidly with time 
because of their relatively short half-lives. The long-lived nuclides, such as 
106 Ru— 106 Rh and 137 Cs, contribute only a small fraction of the dose rate at 
t = 2 weeks but become increasingly significant at later times. At t = 2 years, for 
example, these nuclides account for 85% of the total external gamma dose rate 
of the uniformly deposited fission products. 

In the period from 2 weeks to 2 years, the major fraction of the dose rate is 
from nuclides with half-lives of the order of months which have relatively high 
yields, such as 95 Zr— 95 Nb and 103 Ru. These nuclides account tor more than 
85% of the dose rate at t = 20 weeks and more than 60% of the dose rate at 
t = 50 weeks. These nuclides also account for more than 50% of the total 2-week 
to 30-year dose integral. 

Except for 95 Nb, the 2-week to 30-year dose integrals are computed for 
each significant nuclide by means of Eq. 6 with the physical decay constant 
X = 0. In computing the 95 Nb dose integral, we must consider its growth from 
the decay of 9 5 Zr. Since all other nuclides are produced at early times or have 
short-lived precursors, the change in dose rate with time is due only to 
radiological decay. The sum of all individual contributors gives a total 2-week to 
30-year dose integral of 1124 R/kt/sq mile. 

Since the dose rate decreases rapidly with time, most of the integrated dose 
is delivered at early times postdetonation. For example, during the period from 
2 to 20 weeks, 680 R/kt/sq mile, or more than 60% of the total 2-week to 
30-year dose integral, is delivered. An additional 200 R/kt/sq mile is delivered in 
the period from 20 to 50 weeks. Thus nearly 80% of the 30-year total integrated 
gamma dose is delivered during the first year postdetonation. 



76 



MARTIN AND KORANDA 



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IMPORTANCE OF TRITIUM 77 

COMPARISON OF TRITIUM DOSE WITH EXTERNAL GAMMA DOSE 

The dose rate and the 2-week to 30-year dose integrals for tritium and for 
the gamma-emitting fission products are listed in Table 2 in roentgens per hour 
per kiloton per square mile and roentgens per kiloton per square mile, 
respectively. Table 3 lists the same data, except that here the tritium is assumed 
to have an 18.8-month residence time in the biosphere. It can be seen that in 
both cases the gamma dose rate is very much greater than the tritium dose rate, 
particularly at early times. The dose ratio is the ratio of the fission-product 
gamma to tritium dose rate. 

At early times the dose ratio is about 10 4 , but it decreases rapidly to a ratio 
of about 70 at t = 50 weeks. The decline with time then becomes more gradual 
until a minimum ratio of 7 is reached at about t = 4 years. The ratio then 
increases slowly to a value of about 10 at t = 30 years. When the tritium 
residence time in the biosphere is assumed to be 18.8 months, the dose ratio has 
a minimum value of 50 at t = 2 years. In either case, the fission-product external 
gamma dose rate is always at least 7 times the tritium dose rate. When the 
physical residence time of tritium is considered, the tritium dose rate is never 
more than 2% of the external gamma dose from fission products. 

The comparison of tritium with the external gamma dose from fission 
products can also be made on the basis of the 2-week to 30-year dose integral. 
The dose integral for the fission products is 1 124 R/kt/sq mile; the value for 
tritium is 30 R/kt/sq mile, or 3 R/kt/sq mile when the residence time is 
considered. The fission-product dose integral is thus at least 37 times the tritium 
dose integral and is more likely to be 370 times as much. 

CONCLUSIONS 

This analysis was done on a relative scale. The importance of other internal 
beta emitters and of activation products can be assessed in a similar manner, 
relative to the fission-product external gamma scale. The full significance of the 
fallout-radiation hazard to the survival of man in the event of nuclear attack will 
depend on assessment of the absolute values of dose rate and dose integrals. The 
extent of preventive or corrective measures to be taken against the fallout 
radiation hazard can then be determined. Many hypothetical attack situations 
that go beyond the scope of this paper will have to be considered in making the 
assessment of the absolute hazard. The task can be simplified somewhat by the 
approach presented here, which shows that tritium is relatively unimportant in 
the civil-defense context when compared with the external gamma dose from 
fission products. 

ACKNOWLEDGMENT 

This work was performed under the auspices of the U. S. Atomic Energy 
Commission. 



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MARTIN AND KORANDA 



REFERENCES 



I.E. H. Fleming, Jr., The Fission Product Decay Chains Pu with Fission Spectrum 

Neutrons. Vol. III. Roentgens per Hour per Kiloton per Square Mile vs. Time, USAEC 
Report UCRL-50243, Lawrence Radiation Laboratory, University of California, Mar. 31, 
1967. 

2. J. J. Koranda and J. R. Martin, Persistence of Radionuclides at Sites of Nuclear 
Detonations, in Biological Implications of the Nuclear Age, Livermore, Calif., Mar. 5—7, 
1969, B. Shore and F. Hatch (Coordinators), AEC Symposium Series, No. 16 (CONF- 
690303), pp. 159-187, 1969. 

3. J. R. Martin, C. F. Jordan, J.J. Koranda, and J. R. Kline, Radioecological Studies of 
Tritium Movement in ? Tropical Rain Forest, in Symposium on Engineering with Nuclear 
Explosives, Las Vegas. Nev., Jan. 14-16, 1970, USAEC Report CONF-700101 (Vol. 1), 
pp. 422—438, American Nuclear Society, May 1970. 

4. C. F. Jordan, J. J. Koranda. J. R. Kline, and J. R. Martin, Tritium Movement in a Tropical 
Ecosystem, Bio science, 20(14): 807 (1970). 

5. J. R. Martin and J. J. Koranda, Distribution, Residence Time and Inventory of Tritium in 
Sedan Crater Ejecta, USAEC Report UCRL-72572, Lawrence Radiation Laboratory, 
University of California, Nov. 10, 1970; also Nucl. Tecbnol., in preparation. 



PROPERTIES OF FALLOUT IMPORTANT 
TO AGRICULTURE 



CARL F. MILLER 

The Systems Operations Corporation, Hallock, Minnesota 



ABSTRACT 



The intrinsic properties of fallout associated with radiological hazards which could affect 
agricultural operations in the postattack period of a nuclear war include: (1) the 
radionuclide composition of the fallout material, which determines the energy composition 
of the gamma and beta radiation emitted, (2) the physical and chemical properties of the 
fallout particles (such as size, shape, composition, structure, and solubility) which influence 
their retention by surfaces, and (3) the solubility and biological availability of specific 
radionuclides. In terms of crop or agricultural-product output, both operational factors 
(effects on man and his social system) and biological factors (response of plants and 
animals) would be important. 

Since the degree of the hazard to the food-producing agricultural systems would 
generally depend more on external parameters (such as the available weapon system, form 
or mode of attack, level of attack, explosive yield of weapons, relative heights of burst, and 
local and regional weather patterns) than on the properties of the fallout, these parameters 
are discussed in detail. 

A major recent development in weapon systems which could have a significant impact 
on the type and extent of hazard to agriculture in a nuclear war is the Multiple Independent 
Targeted Reentry Vehicle (MIRV). Estimates of MIRV system capabilities, especially in 
terms of using many smaller-yield warheads on many smaller targets, are used to identify 
several important implications for future civil-defense planning and the role of civil-defense 
capabilities in the relative deterrence posture. If sufficient fallout shelters with protection 
factors of 130 or more were available for the U. S. population, it appears that the U.S.S.R. 
could not deploy sufficient SS-9 missiles to assure the destruction of the U. S. population 
within the next 800 years (even with MIRV) using currently available technology. Also, the 
effect of MIRV and the associated lower-yield warheads would be to almost eliminate the 
widespread fallout effects previously estimated for attacks in which land-surface detonations 
of weapons in the megaton-yield range have been postulated; a comparable degree of effect 
on agriculture might be achieved from attacks that are designed to kill more than 65% of the 
U. S. population if all detonations in rural areas were surface bursts. 

81 



82 MILLER 

The more important properties of fallout which could significantly affect 
agricultural operations after a nuclear war are those related to the total gamma- 
and beta-radiation emissions from the particles and the physical and chemical 
properties of the particles which influence their retention by plant and animal 
surfaces. In addition, physiochemical properties of the fallout, such as the 
solubility of individual radionuclides, can become important radiological-hazard 
problems in the production and consumption of specific agricultural products. A 
well-publicized example of this is the relative solubility of * 3 J I and its 
accumulation in milk produced by cows that have ingested fallout-contaminated 
food and water. 

In terms of radiobiological effects to agriculturally important plants and ani- 
mals, previous analyses have shown that the major cause of radiation damage 
would be the exposure of temporal units of the biota of rural farmland 
ecosystems to ionizing radiation. 1 Under the subject of longer-term ecological 
effects, the major concern would be with the secondary effects to functional 
units of the biosphere including biological populations, communities, and 
ecosystems. Secondary effects, in contrast to direct effects, are disturbances 
and injur\- or damage, usually caused by the direct effects, which do not become 
important or do not develop until some time later. One property of fallout that 
could affect the relative severity of short-term and long-term effects on 
agricultural plants and animals is the combined decay rate of the radionuclides in 
the fallout; another property is the energy spectrum of the absorbed radiation. 



SOURCE OF RADIOLOGICAL INJURY OR DAMAGE 

In a nuclear explosion more than a hundred radioactive fission-product 
nuclides and many additional neutron-induced radionuclides are produced. This 
radioactive mixture initially consists of radionuclides with radioactivity-decay 
half-life values that vary from a fraction of a second to many years. Since most 
of the radionuclides emit both beta particles and gamma rays when they 
disintegrate, these two types of ionizing radiation are present in a fallout 
environment as potential causes of biological damage to living tissue. The 
presence of all these radionuclides in an ecosystem thus constitutes a source of 
radiological hazard from fallout. The major radiological hazard to man is 
external gamma radiation from deposited fallout; this fact requires special 
recognition both in damage-assessment studies and in civil-defense planning. 

Fallout particles from land-surface detonations as nuclear-radiation sources 
consist of fused, sintered, and unchanged grains of soil minerals or other 
materials present at the point of detonation. 3 Also present to a minor extent in 
fallout particles are inert materials from the weapon or warhead, as well as the 
radioactive elements produced in the fission and neutron-capture processes 
occurring at detonation. Roughly, the relative amounts of soil minerals, 
bomb-construction materials, and radioactive elements in fallout particles are 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 83 

(1) up to 1 Mt of soil per megaton of total weapon yield, (2) of the order of 1 
ton of warhead materials per megaton of total weapon yield, (3) about 120 lb of 
fission products per megaton of fission yield, and (4) about 100 to 200 lb of 
induced radioactive atoms per megaton of total yield. 

Analyses of fallout particles from surface and near-surface detonations 
collected at weapons tests at both the Eniwetok Proving Ground and the Nevada 
Test Site show that the radioactive elements are either within the interior of 
fused and sintered particles or are attached to the exterior layers of all three 
types of particles. Larger fallout particles are formed, not by the condensation 
of vaporized soil, but from individual or agglomerated soil particles that 
originally either existed as single soil grains or were produced through the 
breakup of a fused mass of liquid soil or rock. All three types of particles are 
drawn into the rising fireball and apparently serve as collectors for small 
vapor-condensed particles and as condensation centers for vaporized fission- 
product and radioactive neutron-induced atoms. 

On the basis of physiochemical properties of common metallic oxides of the 
chemical elements in soil and coral, it can be concluded that the fallout-forma- 
tion process does not begin until the fireball temperature (or the temperature of 
the gaseous material in the fireball) has decreased to about 3000°K, because at 
higher temperatures all materials tend to dissociate rather than to condense. As 
the fireball temperature decreases below about 3000 K, vapor-condensation 
processes should take place to produce very small liquid particles. Such 
small particles have been observed in worldwide fallout collections and as 
attached particles on unchanged coral grains in the fallout materials collected 
from weapons tests at the Eniwetok Proving Ground. 

As the fireball rises and cools and the crater materials are drawn up into its 
volume, the thermal action at the surfaces of entering molten particles should 
gradually change from a vaporization process to a condensation process in which 
the less volatile fission products condense onto and diffuse into the liquid phase 
of the particles. In addition, the larger molten soil particles, as they circulate 
through the fireball volume, would rapidly form agglomerates with a large 
fraction of the smaller, previously formed, vapor-condensed particles. Particles 
entering the fireball volume at later times may be heated to sintering 
temperature or may never be thermally altered. 

As the surface temperature of the particles decreases, the rate of diffusion of 
the condensed radioactive atoms into the interiors of the particles should also 
decrease so that the more volatile of the radioactive elements, which can 
condense only at lower temperatures, collect and concentrate on the exterior 
surface of the particles. Also, radioactive daughter atoms (even if not volatile) 
formed at later times from volatile parent nuclides, such as those from rare-gas 
elements, would be concentrated on the exteriors of the smaller particles. 
Because of the differences in volatility as a function of temperature among the 
various fission-product elements, fractional condensation would be expected to 



84 MILLER 

occur throughout the whole fallout-formation process. The observed degree of 
solubility and biological availability of such radionuclides as 89 Sr, 90 Sr, and 
137 Cs from the fallout of nuclear-weapons tests strongly supports these views 
regarding the condensation process. 

In general, two rather distinct periods of fallout formation by condensation 
processes have been postulated. 3 In the first period the condensation of volatile 
radioelements is considered to occur by deposition onto and diffusion into large 
molten soil particles and by agglomeration with smaller particles. The radioele- 
ments thus condensed would become fused within the volumes of the molten 
particles when they cooled and solidified. In the second period the remaining 
volatile gaseous radioelements condense onto the surfaces of relatively cold solid 
particles (most of which consist of late-entering, thermally unaltered grains of 
soil). 

The significant chemical property associated with the amount of a 
radioelement that condenses during the second period of formation is its 
potential solubility, whereby it can become biologically available for later 
assimilation by plants and animals. The more volatile radioelements in fallout are 
more soluble and more biologically available than the refractory elements. 
However, the fractional degree to which each element condenses in either period 
of condensation is expected to depend very much on both the temperature and 
the rate of temperature decrease, which determine the conditions and times at 
which diffusion into the particle effectively ceases and at which the condensing 
radioelement begins to concentrate on the surface of the particles. 

If all the materials produced in a land-surface nuclear detonation and all 
entering the fireball volume remained together for the first 5 or 10 min after 
detonation, the radioactive composition and the subsequent radioactive decay 
(and nuclide solubility) would be about the same for all fallout particles. 
However, it is known that all the entering particles do not remain together in the 
fireball and cloud for such periods of time. Immediately after the fireball 
expands to maximum size it begins to rise in the air. The upward movement of 
the hot gases sets in motion a large-scale toroidal circulation because of the drag 
forces of the surrounding air. This toroidal motion, with circulation velocities in 
excess of 100 mph, is probably responsible for setting up air motions whose 
forces are sufficiently strong to pull the blast-loosened soil from the crater and 
crater lip into the rising fireball. 

The circulation of the particles in the toroid should result in rapid separation 
of the larger particles from the circulating mass of condensing gases and should, 
by centrifugal force, move them to the periphery of the toroid. When the 
circulating particles reach the periphery or the bottom of the cloud and the pull 
of gravity begins to exceed the upward drag forces of the air near the base of the 
rising cloud, the particles should begin falling toward the earth. Other particles 
of the same size that are not yet near the periphery of the toroid may continue 
to circulate for a much longer time before they leave the base of the cloud. 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 85 

These views of particle circulation and formation are suggested by (l)the 
relatively long period over which particles of a given size arrive on the ground, 
(2) the relatively early initial arrival times for close-in fallout, (3) the variation in 
composition of the radioelements carried by particles of different sizes, and 
(4) the variation in specific activity and radioelement composition among 
particles of a given size. 

The concentration of the volatile radioelements in the radioactive composi- 
tions carried by the larger particles is generally low. This relatively low 
concentration could occur only through the earlier ejection of the large particles 
from the volume of the fireball containing the radioelements (vapors plus small 
vapor-condensed particles). In addition, the large fallout particles from many 
low tower detonations do not contain or carry any soluble radioelements; 
therefore these particles must have been ejected from the rising fireball or cloud 
when the particle surfaces were still at a very high temperature. Thus the 
toroidal motion is considered to be partially responsible for the observed 
differences in gross radioactive decay and biological availability of different 
radioelements carried by fallout particles of different diameters. 

The toroidal motion, which apparently causes early ejection of the larger 
particles (i.e., early with respect to time-of-fall from the height of the stabilized 
cloud), can also cause prolonged apparent buoyancy of the smaller particles. The 
smaller particles should circulate for longer times and should remain in the 
toroid where they could adsorb the more volatile radioactive elements on their 
surfaces. Essentially all fallout particles, except those with diameters less than 
about 50 to 80 [J., apparently leave the cloud volume under influences of toroidal 
circulation. 

No observed data exist on the properties of fallout from detonations on soils 
similar to those of likely targets in a nuclear war. In fact, only a few detonations 
at the Eniwetok Proving Ground and the Nevada Test Site have provided data 
useful for the development of fallout models for land-surface detonations. All 
the large-yield test devices were detonated over water, on coral atolls, or in the 
air. Most test detonations in the yield range of 1 kt to 1 Mt were mounted on 
towers. Consequently there is no evidence proving that all types of fallout 
information obtained from the weapons tests (even under suitable detonation 
conditions) are satisfactory for evaluating computational procedures developed to 
give quantitative estimates of properties of the fallout particles, as well as of their 
distribution over the country as a consequence of an assumed set of nuclear 
detonations on specified targets in the continential United States. Further 
theoretical developments and supporting experimental work are needed to 
evaluate and improve the validity of some available input data used in the 
formulation of many fallout models. 

The radionuclides in worldwide fallout from high airbursts, in contrast to 
those described for the close-in local fallout from near-surface detonations, are 
generally quite soluble. Therefore essentially all the radionuclides in long-range 
worldwide fallout are biologically available. Fused-type particles formed from 



86 MILLER 

the warhead or bomb materials have been identified and found in fairly large 
numbers in stratospheric collections of bomb debris. 3 But a large fraction of the 
worldwide fallout from a large-yield nuclear airburst is apparently formed in the 
stratosphere at some time after detonation through processes of coagulation and 
coprecipitation of the radioactive atoms with the natural stratospheric aerosol 
particles. These particles, composed mainly of water-soluble ammonium sulfate 
compounds, apparently serve as carriers for eventually returning the longer-lived 
radioactive elements to earth. 

Under all conditions of detonation that lead to the production of fallout, the 
form and properties of the fallout particles are determined during the cooling 
period of the fireball and cloud: for the decay products of gaseous and several 
other radioelements, the attachment to particles occurs at later times. The 
materials in or entering the fireball at these times are particularly important 
factors in determining the properties of the fallout particles. These formation 
processes set the stage for all subsequent radiological interactions between the 
fallout materials and the biological and ecological environments in which they 
deposit. 

One of the chief difficulties in predicting fallout levels at a given location, in 
addition to the problem of defining the fallout-particle-cloud source, lies in the 
problems associated with analyzing and predicting the wind fields. The winds at 
all altitudes through which the particles fall, of course, determine how the 
fallout particles are distributed over the earth's surface. Other major factors for 
which very little accurate data exist, especially for fallout from detonations over 
silicate soils, include (1) variation of the specific activity of fallout with particle 
size and (2) influence of weapon yield, burst height, and environmental material 
(soils and other likely target materials) on the gross particle-size distribution of 
the fallout (i.e., by particle number, mass, or radioactivity content). 

The radiation, chemical, and physical properties resulting from the fallout- 
formation processes and conditions may give rise to one or more of five major 
types of radiological hazard to biological species. These are (1) external gamma 
hazard, as mentioned for humans, (2) contact beta hazard, (3) beta-field hazard, 
(4) internal hazard from ingested radionuclides, and (5) inhalation hazard. 

The nature of the hazard and the response of biological species to it are 
perhaps better known and understood for external gamma radiation than for the 
other four hazards. Under most exposure situations occurring under nuclear war 
conditions, the external gamma hazard would be the major cause of serious 
direct radiation injury to large biological species. 

The contact beta hazard could arise when fresh fallout particles remained in 
contact with biological tissue for some period of time. Humans could easily 
avoid this tvpe of exposure by wiping or brushing fallout particles from exposed 
skin. This hazard would develop only during and shortly after fallout deposition. 
After several days the fallout particles would no longer have the radioactive 
content necessary to cause serious damage to skin tissues. Some data on the 
retention of particles by humans 6 and on skin doses to animals have been 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 87 

reported. No reliable correlations of such data with fallout-deposition levels have 
yet been made, but unverified relations between the two have been proposed. 8 
A few sets of computations and experimental measurements have been made of 
the contact beta dose to plants; data on the retention of fallout particles by the 
foliage of many different types of plants have been reported. 6 

The beta-field hazard (sometimes called the "beta-bath" hazard) could occur 
in certain confined radiation source geometries for humans. It would be 
expected to be severe for small plants, small animals, and insects whose habitats 
become covered with the deposited fallout particles. In such geometries the 
beta-to-gamma ratio (i.e., the rad-to-roentgen ratio) would generally be between 
30 to 100 for fallout-radiation compositions similar to those of past weapons 
tests. No mathematical models on the beta-field hazard to small plants and 
animals or insects are known to exist; however, some related work on this hazard 
was reported. 1 ' The combined radiological hazards (external gamma, contact 
beta, and beta-field) for plants, animals, and insects should be considered in 
future research investigations. 

The internal hazard from ingested radionuclides and the consequent pattern 
of exposure of humans, animals, plants, and insects to this hazard after a nuclear 
war would depend mainly on their uptake and assimilation of biologically 
available (soluble) radionuclides. Several major processes are involved in the 
entry of the radionuclides into food chains (or webs). The internal hazard from 
fallout is characterized mainly by the fact that, at least in humans and other 
large vertebrate animals, most of the radiation sources (e.g., radioactive atoms) 
tend to concentrate in specific body organs and that assimilation occurs 
according to the biochemical properties of specific radionuclides. Thus evalua- 
tions of the internal hazard must consider the behavior patterns of each 
radioelement in the fallout. Data on absorbed doses from ingestion of 
radionuclides bv adult humans have been developed in a significant research 
effort conducted by Morgan and co-workers 1 " over the past 15 years. Similar 
sets of data for the absorbed doses for young people during their growing years 
have yet to be developed. Kulp et al. 1 3 developed a bone model for the uptake 
of 90 Sr in worldwide fallout. Models for estimating the absorbed dose from 
assimilation of radionuclides in organs of humans have been developed. 14 

The inhalation hazard would be associated with the inhalation and 
deposition in the respiratory system of small fallout particles of a narrow size 
range. All the available data on exposure of animals in fallout areas at weapons 
tests and in laboratories, on air-filter samples in various fallout environments, 
and on fallout-particle resuspension in air give negligible results for the 
inhalation hazard. Therefore this hazard is considered to be minor relative to 
other possible radiological hazards. 

The major primary radiological hazards that apparently would cause most 
damage to farmland (and wild land) ecosystems are external gamma and beta 
radiation and internal beta radiation from assimilation of radionuclides. It is 
significant for biological repair and recovery processes that injury sustained from 



88 MILLER 

external radiological hazards under nuclear war conditions would generally be 
more comparable to an acute assault than to a chronic assault, whereas the 
assimilation of radionuclides would be mainlv a chronic exposure to low levels 
of nuclear radiation. The general effect of radionuclide cycling in species of 
ecosystems appears from all available data to be mainly a long-term public-health 
problem rather than a cause of injury leading to the death of biological species. 
Because of the large variability in the radiosensitivity of plants according to 
species, age, and period between growth and reproduction cycles, the gross 
effects in plant population from exposure to gamma radiation would depend a 
great deal on the time of year, perhaps of month, when an attack occurred. Thus 
the total consequence would depend on the targeting pattern for many 
agricultural areas; the Midwestern states, for example, could receive high levels 
of fallout from high-yield surface detonations on missile sites in neighboring 
states and in the Rocky Mountain area. 

RADIOLOGICAL DAMAGE ASSESSMENTS 
Current Weapons Systems 

In most damage-assessement analyses, military targets normally play an 
important role in establishing the pattern of weapon delivery for any 
hypothetical attack. For many military targets it is appropriate to assume 
ground-surface detonations to assure destruction of the target components. 
Therefore in such attack patterns, called counterforce attacks, a large amount of 
local fallout is produced. Furthermore, in such studies rather large weapon yields 
are customarily assigned to military targets, perhaps for consistency with the 
assured destruction concept.* The relative area of the continental United States 
within a given standard (H + 1) exposure-rate contour (using an open-field 
radiation source as the reference condition) as a function of attack level in total 
megatons detonated is shown in Fig. 1 (Ref. 15). The relative area of the 
continental United States at a given attack level is shown in Fig. 2 as a function 
of the standard exposure-rate-contour level. 

For hypothetical nuclear attacks on the United States in which most 
individual weapon yields are assumed (or assigned) to be in the range of 1 to 
10 Mt, pure counterforce attacks at attack levels very much larger than 
10,000 Mt would not be realistic, at least on a first-strike basis, because of the 
limit in number of military targets. Thus the extrapolation of the solid lines in 
Fig. 1 to the higher attack levels probably does not represent any real situation. 



*The assured destruction concept is an extension of the notion that a weapon system or 
attack pattern can be designed or deduced to perform as envisioned by calculation, within a 
specified degree of assurance or a stated degree of reliability, ipso facto. The concept is to 
some degree a technical embellishment evolved by military technicians and analysts to 
provide a logical basis for deterrence policies. 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 



89 



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FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 91 

As a general guide, I s values up to 10 R/hr at 1 hr for fallout from fission 
weapons do not represent a serious direct radiological hazard to humans or to 
most other biological species. At I s values greater than 100 R/hr at 1 hr, 
extended (but variable) stay times in shelter generally would be required to 
avoid possible effects of radiation sickness to humans. The I s values of about 
1000 R/hr at 1 hr and greater represent a serious radiological hazard for a fairly 
long time after attack; sickness and possible fatalities among poorly sheltered or 
unsheltered people could result. For I s values of 10,000 R/hr at 1 hr and greater 
(radiation levels that generally would occur only as a result of overlapping 
fallout patterns), survival would be possible only in the best available fallout 
shelters with facilities for an extended stay time plus decontamination 
requirements for a reasonably short reoccupation time after attack. 

For the weather conditions usually assumed for the hypothetical counter- 
force and mixed attacks (the latter may include some ground bursts on 
urban targets) with a total delivered explosive yield of less than about 
10,000 Mt, the areas within extremely high I s contours would enclose less than 
10% of the land area of the United States, and essentially all such areas would be 
rural forested or agricultural areas. Since the current Soviet nuclear force 
capability is estimated to be more than 10,000 Mt, 15 the delivery of such a 
force in a counterforce or mixed attack such as those represented in Figs. 1 and 
2 would likely involve the coverage of more than 40% of the continental United 
States by I s values of 100 R/hr at 1 hr and more than 25% of the area by I s 
values of 1000 R/hr at 1 hr. Although these relative coverages of the land area 
are rather large, the associated degree of damage to or decrease in the yield of 
specific agricultural products by the respective exposures cannot be deduced 
from the curves of Figs. 1 and 2. To deduce damage, the relative geographic 
locations of the crops, targets, and assumed points of detonation, along with the 
meteorological inputs for each hypothetical attack must be considered; this 
procedure has been used in recent analyses. 1 6 

Future Weapon Systems 

Over the past several years, one of the major developments in weapon 
systems has been the Multiple Independent Targeted Reentry Vehicle (MIRV). 
Certain information and estimates of apparent U.S.S.R. and U. S. progress and 
capabilities in the development of MIRV systems, especially with respect to their 
missile-carrying capacities, have been released to the press by various Department 
of Defense officials, including Secretary Laird. The following statements on 
Soviet nuclear force capabilities and MIRV system characteristics were provided 
by William Beecher 1 7 in a special article in the New York Times, Oct. 28, 1969: 

•As recently as last November, for example, the intelligence community 
predicted that the Soviet Union would stop deploying more interconti- 
nental missiles when they had roughly equaled the 1054 in the American 
arsenal. 



92 MILLER 

•The Soviet Union has in place or going into place about 13 50 inter- 
continental ballistic missiles, roughly 300 more land-based units than the 
United States and 150 more than reported by American officials last spring. 

•The Soviet Union has been testing a new swing-wing medium-range bomber, 
presumably for use against targets in Western Europe and Asia, even though 
it already has a fleet of 750 medium bombers. With aerial refueling, the new 
bomber could be used on round-trip strikes against the United States. 

•The Russians are testing a new medium-range ballistic missile, though they 
alread\' have more than 700 such missiles aimed at targets in Western 
Europe and Asia. 

•The SS-9 can carry a single warhead of from 9 to 25 Mt (9 to 25 million 
tons of TNT) or three warheads of 4 to 5 Mt each. The SS-11 carries a 
warhead of 1 Mt, similar to the payload of the Minuteman missile. 

•John S. Foster, Jr., the Pentagon's research and development chief, said that 
420 SS-9's carrying three separately targetable warheads with one-quarter- 
mile accuracy could destroy about 95°o of the 1000 Minutemen in their 
underground silos. 

• The Soviet Union is now believed to have about 280 such giant missiles in 
various stages of construction. At the present rate of deployment, they 
could have the Minuteman killer force in three more years. 

•The Minuteman-3 is designed to carry three warheads of about 100 kt, and 
the Poseidon submarine-based missiles, 10 warheads of 30 to 40 kt each. By 
comparison, the Soviet SS-9 is being tested with three warheads of about 
5 Mt each, 50 times more powerful than each Minuteman-3 warhead. 

On Jan. 6, 1970, the Washington Daily News, under a dateline from London, 
quoted the following statements: 

• The Institute of Strategic Studies said the Soviet Union should have the 
capability to fit multiple nuclear warheads to its most powerful rockets by 
1973. 

•The influential study group, specializing in international defense devel- 
opments, said the Soviets could have 500 of the multiple-warhead missiles 
ready for use by 1975. 

• The multiple warheads are to be fitted to SS-9 Scarp rockets, "extremely 
powerful" three-stage missiles with a maximum range of 9800 miles, the 
report said. It estimated that each launcher cost between $25 and S30 
million. 

• About 250 of the SS-9's are believed to have been installed already in the 
Soviet Union, but these are not armed with the multiple warheads, the 
institute said. 

• The Soviet SS-9 rocket originally was designed to carry a single warhead of 
between 10 and 25 Mt. 

On January 7, 1970, Secretary of Defense Melvin Laird provided the 
following information to newsmen: 



FALLOUT PROPERTIES IMPORTANTTO AGRICULTURE 



93 



The Russians could have a knockout missile force in place earlier than the 
1974 period forecast to Congress last year. 

The discussion centered around Laird's estimate last summer that the 
Soviets could have about 420 of the huge SS-9 missiles in readiness by 1974. 
Such a force, Laird said then, could destroy 95% of this country's 
Minuteman missiles in a surprise first attack. 

He declined to say how many of the SS-9's, capable of hurling a single 25-Mt 
warhead or three warheads of 5 Alt each, are now in place or under 
construction. There have been unofficial estimates running up to about 279. 



Defense officials, the news media, prominent scientists, and politicians have 
repeated similar information to the public over the past 10 months or more. The 
statements indicate that for the SS-9 missile the number of warheads apparently 
depends on the explosive yield of each warhead according to the relation 



866W" 



(1) 



where n m is the maximum number of warheads carried by the missile and W is 
the explosive yield of each warhead. Similarly, for the Minuteman-3 missile 



n m = 65 W 



(2) 



and for the Poseidon and SS-11 missiles 



n m = 100W 



(3) 



Values of n m for the SS-9 missile, the maximum explosive load, and the 
total target area enclosed by the 35-psi overpressure contour for selected 
warhead yields are given in Table 1 (for the case where all weapons are airburst 
at the height for which the area enclosed by the selected overpressure contour is 



Table 1 
CALCULATED VALUES FOR SS-9 MISSILE' 



w 


11 m 


n m W 


A m (35 psi) 


/megatons\ 


/warheads \ 
\ missile / 


/megatons \ 


^sq miles^ 


\ warhead / 


\ missile / 


\ missile / 


0.1 


40 


4.0 


31.8 


0.3 


19 


5.7 


31.4 


1.0 


8 


8.0 


29.5 


3.0 


4 


12.0 


30.7 


10.0 


1 


10.0 


17.1 


25.0 


1 


25.0 


31.9 



94 MILLER 

maximized and at ground zero locations that are arranged in a hexagonal pattern 
in which the overpressure contours overlap in such a way that no point within 
the target receives less than 35 psi). 

Table 1 shows that A m (35 psi) is maximum at values of W which yield 
integer values of n m in Eq. 1. For n m equal to 2.0 warheads per missile, for 
example, W is 9.0 Alt. For this yield A m (35 psi) is 31.9 sq miles/missile, 
although r or the single 10-Mt warhead selected, A m (35 psi) is only 17.1 sq 
miles/missile. In this case additional smaller warheads could be added to the 
capacity of the missile as appropriate to increase the value of A m over that 
given. If the target area is less than 30 to 32 sq miles and n m is more than 2, 
decoys could be used to replace some of the warheads. 

Neglecting any possible effect of decoys and of active defense capabilities, 
the MIRY system using a maximum number of warheads, in contrast to a single 
warhead of maximum yield, apparently would provide no advantage in 
decreasing the number of missiles for imposing a selected minimum overpressure 
on a single target on an area basis. However, if the shape of the target area is 
considered, MIRV system weapons could achieve area enclosure within a 
selected overpressure contour with a smaller number of missiles and a smaller 
total explosive yield than could a single-warhead missile system. For example, a 
single SS-9 missile loaded with 40 100-kt warheads (4.0-Mt total yield) could, 
according to Table 1. enclose an area about 32 miles long and 1 mile wide within 
the 3 5-psi contour. Lengthwise coverage by the same overpressure contour 
would require five SS-9 missiles if each carried a single 25-Mt warhead (125-Mt 
total yield). 

If the MIRV system could be employed with essentially no constraint on 
warhead dispersion among neighboring targets and if full use could be 
made of such capabilities to deliver warheads to targets, then any set of 
estimates of single-weapon missile force requirements may be directly converted 
to missile requirements for a system with MIRY. Under such conditions 
estimates of the number of SS-9 missiles required to cause specified levels of 
fatalities among the 1970 U. S. population sheltered in wood-frame structures 
exposed to selected minimum overpressures are given in Table 2 for weapon 
yields of 0.1, 1.0, and 10 Mt.* The lowest number of missiles for a given 
percentage of fatalities always occurs for a weapon yield of about 100 kt or less 
for the urban-center target areas. 20 Thus the general dependence of missile 
requirements on fatalities or area by a given overpressure contour relative to 
target size apparently ceases to be important for weapon yields less than about 
100 kt. This independence is shown especially for the smaller high-density urban 
areas that would comprise the first set of targets for an antipopulation attack; a 
similar situation pertains for the smaller urban target areas listed in Table 2 in 
the range of 55 to 65% of the total population. 



*These estimates are based on information from the Japanese experience at Hiroshima 
and Nagasaki in World War II as discussed in Refs. 15, 18, and 19. 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 



95 



Table 2 

ESTIMATED MINIMUM NUMBER OE SS-9 MISSILES WITH MIRV REQUIRED FOR 

SPECIFIED LEVELS OF FATALITIES AMONG THE 1970 U. S. POPULATION 

SHELTERED IN WOOD-FRAME STRUCTURES 









Minimum overpressure 




Fatalities, % 


5 psi 


10 psi 


15 psi 


20 psi 


35 psi 






W = 


0.1 Mt 






20 


633 


128 


87 


82 


119 


30 


2,645* 


528 


220 


184 


250 


40 




5,770 


470 


348 


47 3 


50 




21,820* 


4,698 


533 


770 


60 






16,850 


4,450 


1,06 3 


70 






32,550* 


12,210 


5,310 


80 








51,630* 


15,590 


100 




W = 


1.0 Mt 




115,500* 


20 


1,237 


187 


114 


100 


137 


30 


10,950* 


1,094 


270 


223 


292 


40 




6,615 


903 


420 


542 


50 




24,020* 


5.454 


833 


870 


60 






18,530 


5,06 3 


1,179 


70 






35,430* 


13,520 


5,832 


80 








55,930* 


16,920 


100 




W = 


= 10 Mt 




124,500* 


20 


6,848 


924 


427 


340 


3 24 


30 


23,570* 


1,541 


1,408 


707 


669 


40 




16,260 


6,178 


1,707 


1,173 


50 




46,000* 


14,010 


5,008 


2,208 


60 






36,520 


13,290 


4,319 


70 






65,610* 


26,910 


14,270 


80 








100,900* 


33,360 


100 










218,800* 



Ff(max) is 0.28 at 5 psi, 0.45 at 10 psi, 0.62 at 15 psi, 0.80 at 20 psi, and 1.00 at 35 psi 



In other words, a further significant reduction in overkill and wastage of 
explosive energy associated with the detonation of large-yield weapons on small- 
size targets would not be achieved by the use of weapons with yields less than 
100 kt on U. S. urban centers as a target system. However, for attacks designed 
to cause more than about 65% fatalities under the conditions assumed in 
Table 2, the various states or the country as a whole would become a single 



96 MILLER 

target, and on an area basis the number of missiles required would be essentially 
independent of weapon yield for missiles carrying maximum payload. 

The Soviet's estimated 1970 intercontinental nuclear force, from the 
previously quoted statements, is approximately 11,000 Alt, assuming a one-way 
mission or refueling of 750 bombers carrying a payload of 5 Alt each, 1100 
SS-ll's carrying 1 Alt each, and 250 SS-9's carrying 25 Alt each. These estimates 
do not include the submarine force of perhaps 200 vessels, because it is assumed 
that its mission would be that of a reserve or second-strike force. Such a ready 
force, if delivered in an antipopulation attack with 100% reliability and accuracy 
in the most efficient manner (i.e., by allocating the 1 -Alt weapons to densely 
populated cities with small areas and the 25-Alt weapons to less densely 
populated urban centers covering larger areas) utilizing full-target coverage by 
20- or 35-psi overpressure contours, could result in fatalities amounting to about 
42% of the population if all were sheltered in wood-frame structures. This 
percentage of fatalities is equivalent to the entire 1970 population of the 680 
largest U. S. cities. 

If this same nuclear striking force were converted to efficient and 
maneuverable MIRV systems with 100-kt warheads, the single 5-Alt warhead 
assumed for the bombers would convert to thirteen 100-kt warheads; the single 
1 -Alt warhead taken for the SS-11 would convert to four 100-kt warheads; and 
the single 25-Alt warhead for the SS-9 would convert to about forty 100-kt 
warheads. The combined striking power for these warheads is then 2375 Mt, 
which, if delivered according to the assumptions in Table 2, could produce about 
52% fatalities among the 1970 U. S. population. This combined nuclear striking 
force would be equivalent to a total of 593 deployed SS-9 missiles with the 
A1IRV system, all armed with 100-kt warheads. 

Assuming such an SS-9 MIRV force to be in existence, estimated minimum 
deployment times and costs in 1970 U. S. dollars for both the total and 
additional SS-9 missiles (each fitted with 40 100-kt warheads) required to cause 
stated relative fatality levels among the 1970 U. S. population for the conditions 
of Table 2 are given in Table 3. The year of final deployment is based on the 
assumption of both a constant rate of production and one that increases linearly 
from 5 to 100 missiles per year from 1970 to 1980. 

Note that the calculations are based on the 1970 U. S. population 
distribution; thus, for the fatality percentage having Y Y and Y 2 values 
significantly larger than 1970, the number of required missiles, the values of Y { 
and Y 2 , and the added cost are all underestimates (except for the 100% level of 
fatalities). Since the estimated number of missiles refers to weapons delivered on 
target, these figures are, by definition, underestimates of force requirements for 
the stated fatality levels. 

These estimates suggest that at the current rate of production the most 
economical and effective SS-9 MIRV system could not impose, through air-blast 
weapons effects, the current popular view of assured and complete destruction 
of the 1970 U. S. population in a nuclear attack until sometime after the year 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 



97 



Table 3 

ESTIMATED NUMBER OF SS-9 MISSILES WITH MIRV, YEAR OF FINAL 

DEPLOYMENT, AND COSTS FOR CAUSING A STATED PERCENTAGE OF FATALITIES 

AMONG THE 1970 U. S. POPULATION BY BLAST EFFECTS ON PEOPLE 

IN WOOD-FRAME STRUCTURES 





Total required 


Add 


itional required 








Fatalities, 


number of SS-9 


number of SS-9 


Y? 


vt 


Added cost. 


% 


missiles 




missiles 


(year) 


(year) 


10 9 $ (U. S., 1970) 


20 


80 












30 


180 












40 


340 












50 


5 30 












60 


1,060 




467 


1979 


1977 


13 


70 


5,310 




4.717 


2064 


2005 


130 


80 


15,600 




15,010 


2270 


2037 


413 


90 


38,700 




38,110 


2732 


2084 


1050 


100 


115,500 




114,900 


4268 


2175 


3200 



Yj = 0.02N + 1958, at a constant rate of 50 SS-9 missiles per year. 



t = Y 2 - 1970. 



3000. With a constantly increasing rate of production of the missile system, 
however, the force required for such a level of fatalities might be assembled and 
deployed in 100 to 200 years. The cost of such a system could be two times the 
estimated $3 trillion (1970 dollars); this is about 1000 times the current yearly 
Gross National Product of the U.S.S.R. 

Methods for estimating the intermediate-range fallout from 100-kt-yield 
weapons detonated as airbursts to give maximum area coverage of a given 
overpressure contour are not immediately available. Thus the general extent or 
degree of the radiological hazard to agricultural areas downwind from any of the 
larger urban centers hit in such an attack cannot be given. 

The effects of detonating the 100-kt weapons at ground level were 
investigated in an alternate assumed attack mode. This alternative is suggested 
since the fallout levels in the vicinity of ground zero appear to be maximized at a 
yield of around 100 kt. The areas enclosed by exposure-dose contours of 400 
and 1200 R over a period of 100 hr after fallout arrival for 100-kt-yield (100% 
fission) and 1-Mt-yield (50% fission) surface detonations are shown in Fig. 3. 
The 400-R contour indicates generally the limiting extent (outer boundary) at 
which a significant number of persons sheltered in wood-frame houses would 
experience radiation sickness. The 1200-R contour indicates generally the 
limiting boundary at which essentially all persons sheltered in wood-frame 
houses over the specified 100-hr period would eventually die. In other words, all 



98 



MILLER 



o -o 

z 

< 

n 10 



10 



. I Potential exposure dose greater than 1200 R in 100 hr after fallout arrival 
; ] Potential exposure dose greater than 400 R in 100 hr after fallout arrival 




10 



15 



20 



25 



30 



20 



30 40 50 

DISTANCE, miles 



60 



W = 100 kt 

B = 100% fission 

v W = 25 mph 



35 



40 



45 




W = 1 Mt 

B = 50% fission 

v W = 25 mph 

70 80 90 



Fig. 3 Area enclosed by exposure-dose contours of 400 and 1200 R for fallout 
from 100-kt- and 1-Mt-vield surface detonations. 



persons in the shaded area of Fig. 3 who were in shelters with a protection factor 
of 2 (or more at central locations) would become fatalities. 

The full significance of the total fallout-radiation hazard within the two 
elliptically shaped areas, in terms of number of fatalities, cannot be readily 
incorporated into the described antipopulation attack patterns (in which the 
only hazard considered was blast overpressure from air detonations) without 
using a large-scale computer program. However, a conceptional view of the 
relative hazard to people in small wood-frame structures can be obtained from 
simple arithmetic estimates if only the circular portion of the potentially lethal 
area around ground zero is considered. The radius of this area is 1.9 miles for the 
100-kt detonation and 2.5 miles for the 1-Mt detonation. Thus the potential 
lethal radius for the fallout hazard from the 100-kt surface detonation under the 
assumed exposure conditions is 3.4 times the lethal radius for the overpressure 
hazard from the 100-kt air burst (the area ratio is almost 12 to 1). In 
comparison, these radius and area ratios for the 1-Mt detonation are only 2.1 
and 4.4, respectively. Another way of stating the relative extent of these two 
hazards for the specified exposure conditions is that the area coverage of the 
100% lethal fallout level from a 100-kt surface burst is equal to that of the 
overpressure effects from a 4-Mt air detonation. 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 



99 



For people inside concrete buildings with a protection factor of 100, the 
radius of the 600-R lethal-exposure dose from ground-zero-region fallout from 
the 100-kt surface detonation is almost 0.5 mile, only slightly larger than the 
radius of the 48-psi contour (100% lethal for occupants of concrete structures) 
for the 100-kt air burst. The same relative potential hazard from fallout does not 
occur for the 1-Mt surface detonation since the absolute magnitudes of the 
fallout levels near ground zero are smaller in this case; also, the time of fallout 
arrival is shorter for the smaller-yield detonation. 

The general dispersion of ground-zero- and downwind-fallout patterns, as 
represented by the 1200-R potential-exposure-dose contour, for closepacking of 
the ground-zero patterns to cover circular-shaped urban areas is illustrated in 
Figs. 4 and 5. In these figures A T is the largest inscribed circular area enclosing 
an urban target area, and A R is the area within the downwind 1200-R 
exposure-dose perimeter for fallout from cloud altitudes. Figure 5 shows that 
A T for 16 and 28 detonations includes a portion of several cloud-fallout 
patterns; in addition, the maximum downwind extent of the perimeter of the 




W = 100 KT 

B = 100% FISSION 



'W 



= 25 MPH 



179 SQ MILES 



72.2 SQ MILES 



Fig. 4 Geometric configuration of Aj and Ar for the 1200-R exposure-dose 
perimeter when Aj is equal to the maximum circular area covered by seven 
overlapping ground-zero fallout patterns. 



100 



MILLER 




A R (7) = 184 SQ MILES 
A R (16) = 304 SQ MILES 
A R (28) = 439 SQ MILES 



A T (7) = 66.5 SQ MILES 
A T (16) = 200 SQ MILES 
A T (28) = 400 SQ MILES 



Fig. 5 Geometric configuration of Ay and Ar for the 1200-R exposure-dose 
perimeter when Aj is equal to the maximum circular area covered by 7, 16, 
and 28 overlapping ground-zero fallout patterns. 



1200-R exposure-dose contours is essentially constant and independent of the 
size of the circular target. 

The average, or midrange, values of A T and A R are plotted as a function of 
the number of weapons detonated (or the number of ground-zero patterns) 
giving full circular coverage of the target area. No real, single, smooth curve of 
A T and/or A R as a function of the number of detonations or weapons exists for 
target-area coverage requiring one to seven weapons per target. The curves in 
Fig. 6 tend to follow midrange values of A T and A R ; as the number of weapons 
per target increases, the percentage spread in possible values of these two 
parameters decreases. The curves in Fig. 6 were used to estimate the number of 
weapons per target required to enclose each of the 500 largest U. S. cities or 
urban places within the 1200-R contour and the relative amount of land area 
outside the urban areas that would also be enclosed (assuming no overlapping of 
the fallout patterns from these targets and no loss of fallout to areas outside the 
country). The calculated cumulative explosive yield of the 100-kt weapons, the 
total rural land area enclosed, and the number of people involved (i.e., those 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 101 



1000 



100 



10 



n 



i i — n 




j i i i i i 1 1 



i i i i i i m 



1.0 



10 



NUMBER OF WEAPONS PER TARGET 



100 



Fig. 6 Variation of Aj and Ar with number of weapons detonated or 
number of ground-zero fallout patterns. 



residing in the area given by A T who would be fatally involved if sheltered in 
wood-frame houses) are given in Table 4. 

The calculations in Table 4 indicate that, for the 500 most densely 
populated cities or urban places, coverage of the respective A T with at least the 
1200-R exposure-dose contour could be accomplished with a total explosive 
yield of about 103 Mt (i.e., 1030 delivered weapons yielding 100 kt each) and 
that almost 1.0% of the land area of the United States outside the cities would 
be enclosed within the specified 1200-R exposure-dose contour. As shown, the 
500 most densely populated cities or urban places contain about 35% of the 
1970 U. S. population; the estimated number of 100-kt airbursts required to 
cause 35% fatalities by air-blast effects among the population sheltered in 
wood-frame structures would be about 14,000. 

Thus, if the major portion of the U. S. population were in shelters with a 
protection factor of 2 at the time of attack, the number of SS-9 missiles with an 



102 MILLER 

Table 4 

CUMULATED TOTAL YIELD OF 100-KT SURFACE BURSTS 

TO ENCLOSE THE 50 TO 500 MOST DENSELY POPULATED CITIES 

AND NEARBY RURAL AREAS WITHIN THE 1200-R 

EXPOSURE-DOSE CONTOUR 



Target 




Ar, 


A R /3.6 x 10 4 , 


Cumulated percent 


number 


M, Mt 


sq miles 


% 


of 


total population 


50 


15.2 


4,470 


0.12 




12.8 


100 


23.3 


7,520 


0.21 




15.9 


200 


41.5 


14,190 


0.39 




21.4 


300 


62.3 


21,240 


0.59 




27.1 


400 


79.0 


27,690 


0.76 




30.4 


500 


103.4 


35,750 


0.99 




35.0 



idealized MIRV system and 100-kt weapons required to cause a given level of 
fatalities would be about a factor of 13.5 less for an attack in which all 
explosions are ground bursts instead of airbursts (i.e., if the fallout effect instead 
of the air-blast effect were used against the population). This result suggests that, 
without reasonably good fallout protection in the cities, the planned use of 
surface-detonated 100-kt weapons could reduce the time scale required to 
construct a force that could assuredly destroy the 1970 U. S. population from 
about a century or two to about a decade or two (especially if all technical 
problems of production of such a force would be solved without causing 
extended delays in deployment). 

This rather high relative degree of potential effectiveness of the fallout 
hazard from the 100-kt surface detonation could, of course, be countered by the 
provision and use of shelters with protection factors higher than 2. Increasing 
the protection against the fallout radiation would decrease the lethal radius from 
fallout radiation. In turn, a larger number of warheads and missiles would be 
required to accomplish the same level of population destruction by either fallout 
radiation or air blast. The times for producing the needed force would then be 
increased beyond the minimum of the decade or two indicated previously. For a 
shelter protection factor of 130, the 100% lethal radius for the very close-in 
fallout from a 100-kt true surface burst would be equal to the 100% lethal radius 
for the population sheltered in concrete buildings subjected to the air-blast 
overpressure from a 100-kt airburst. In such a protective posture, the limiting 
force requirements for assured destruction of the 1970 population would be 
160,000 SS-9 missiles carrying 100-kt warheads with MIRV's for the smaller 
targets. Such a force, built at the previously assumed rates which increase 
continuously with time, could be deployed approximately by the year 2760 at a 
cost of about $4.5 trillion (1970 U. S. dollars). 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 103 

The apparent advantage of the reduction in force requirements gained when 
lower-yield warheads with MIRV are allocated to small urban places, missile 
sites, and other military targets, together with the fact that area coverage for the 
circular prompt weapons-effect contours is independent of weapon yield, could 
suggest a gradual conversion of existing stockpiled weapons to lower-yield 
warheads in all nuclear arsenals soon after MIRV capabilities become opera- 
tional. If this is the case, some major changes in civil-defense policies, programs, 
and operational plans could be considered to provide an appropriate response to 
salient features of the revised-force capabilities. Two major options are: (1) the 
provision of increased protection to the population and to other resources in 
urban areas against the prompt weapons effects (i.e., blast, thermal, shock, and 
initial nuclear radiation) and (2) the evacuation of cities when there is sufficient 
warning time. The first option would include the provision of shelters with a 
minimum protection factor of 130 to negate the advantage of the 100-kt surface 
burst. For the second option, some difficulties could occur if ground bursts were 
used; however, the downwind extent and width of the fallout pattern from the 
100-kt surface detonation is much less than that from detonations in the 
megaton-yield range, as shown in Fig. 3. This associated reduction in fallout 
areas for attack patterns including only urban-area targets (65% or less of the 
1970 population) would leave essentially all the rural areas and the agricultural 
sector free of direct exposure to any weapons effects. If shelters were available 
in urban areas, postattack evacuation to rural areas free of fallout would be a 
feasible operational alternative. 

As previously mentioned, exposure doses from fallout radiation near ground 
zero are greater for detonations with yields close to 100 kt because of the early 
fallout arrival times and the rather heavy local deposits surrounding the point of 
detonation. Further insight into these ramifications of the fallout hazard would 
require a more detailed analysis than that given here; such an analysis could be 
readily accomplished with the aid of computers. Specific consideration of the 
people, animals, and plants that could be exposed to radiological hazards from 
the downwind fallout has been neglected here. However, practically no human 
fatalities would occur from fallout in the downwind area from the 100-kt 
surface burst if shelters with a protection factor of 130 were available and were 
used. In the described antipopulation attacks (similar results would apply to a 
pure counterforce attack), the downwind boundary of the 1200-R exposure- 
dose contour extends a distance of 20 to 30 miles from the downwind edge of 
the urban areas. Thus the size of the rural farm areas receiving moderately heavy 
fallout levels from the 100-kt surface bursts would be approximately equal to 
the size of the urban areas subjected to direct attacks. Consequently agricultural 
problems caused by fallout would be limited to regions near target cities or 
target military installations. This pattern would persist until more than about 
65% of the population (all urban places) was involved. For much heavier attacks, 
with 100-kt-yield ground-burst weapons, however, the radiological effects on 



104 MILLER 

agriculture could approach those predicted for the counterforce and mixed 
attacks using larger-yield weapons. 



SUMMARY AND CONCLUSIONS 

The intrinsic properties of fallout associated with radiological hazards which 
could affect agricultural operations in the postattack period of a nuclear war 
include: (1) the radionuclide composition of the fallout material, which 
determines the energy composition of the gamma and beta radiation emitted, 
(2) the physical and chemical properties of the fallout particles (such as size, 
shape, composition, structure, and solubility) which influence their retention by 
surfaces, and (3) the solubility and biological availability of specific radio- 
nuclides. In terms of crop or agricultural-product output, both operational 
factors (effects on man and his social system) and biological factors (response of 
plants, animals, birds, and insects) would be important. 

The degree of the hazard to the food-producing agricultural systems would 
generally depend more on external parameters, such as the available weapon 
system, form or mode of attack, level of attack, explosive yield of weapons, 
relative heights of burst, and local and regional weather patterns, than on the 
properties of the fallout. The latter would tend to influence the form rather than 
the degree of the hazard. 

A major recent development in weapon systems that could have a significant 
impact on the type and extent of hazard to agriculture in a nuclear war is the 
Multiple Independent Targeted Reentry Vehicle. Indeed, estimates of MIRV 
system capabilities, especially in terms of using many smaller-yield warheads on 
many smaller targets, may be used to identify several important implications for 
future civil-defense planning. One estimate involves the relatively high levels of 
the fallout hazard near ground zero, which apparently has a maximum for a 
surface detonation at a yield of about 100 kt. The implication of this effect on 
weapon-system cost and times of deployment for the Soviet Union and its SS-9 
missile system is that, if the U. S. fallout-shelter system were poor and a 
majority of people had to remain in their houses during an attack, the Soviets 
could build and deploy at a cost of about $30 billion within the next 10 to 20 
years a nuclear force of sufficient capability to essentially assure the destruction 
of the entire U. S. population. In this case "sufficient capability" refers to the 
use of the force in an antipopulation attack in which local fallout would be the 
main cause of fatalities. On the other hand, if fallout shelters with protection 
factors of 130 or more were available and were used, no advantage in force 
requirements would accrue by the use of surface bursts. Instead, the more 
reliable overpressure effects would be used. In the limit, the assured destruction 
of the U. S. population by blast effects would require at least 160,000 SS-9 
missiles. Even at reasonable increases in production rates, the Soviets would have 
difficulty in deploying such a force within the next 800 years (using currently 



FALLOUT PROPERTIES IMPORTANT TO AGRICULTURE 105 

available technologies); the cost of such a force would be prohibitive at more 
than $4.5 trillion (1970 U. S. dollars). 

The major implication for agricultural systems of the possible use of MIRV 
and the associated lower-yield warheads in a nuclear war is that the fallout 
would be of the intermediate or worldwide type for attacks in which air-blast 
effects are emphasized and that, where the fallout effects are emphasized by use 
of ground bursts, the heavy downwind deposits of local fallout would be limited 
to a distance of about 30 miles from the downwind edge of any target 
independent of the size of the target. In other words, the effect of MIRV and 
the associated lower-yield warheads would be to almost eliminate the widespread 
fallout effects previously estimated for attacks in which land-surface detonations 
of weapons in the megaton-yield range have been postulated. With the described 
Soviet SS-9 missile system with MIRV capabilities, a comparable degree of effect 
on agriculture might be achieved from attacks designed to kill more people than 
the entire U. S. urban population (i.e., more than 65% of the 1970 U. S. 
population) in which all detonations programmed for the rural areas would be 
surface bursts. Further detailed calculations are required before the potential of 
such an attack to cause significant adverse effects on agriculture can be 
evaluated, given the current public fallout-shelter system as a basis for estimating 
population survival. 



REFERENCES 

l.C. F. Miller and P. D. LaRiviere, Introduction to Longer-Term Biological Effects of 
Nuclear War, SRI Project IMU-5779, Stanford Research Institute, 1966. 

2. R. B. Piatt, Ecological Effects of Ionizing Radiation on Organisms, Communities, and 
Ecosystems, in Radioecology, Reinhold Publishing Corporation, New York, 1963. 

3. C. F. Miller, Fallout and Radiological Countermeasures, Vols. I and II, SRI Project 
IMU-4021, Stanford Research Institute, 1963. 

4. K. H. Larson and J. W. Neel, Summary Statement of Findings Related to the 
Distribution, Characteristics, and Biological Availability of Fallout Debris Originating 
from Testing Programs at the Nevada Test Site, USAEC Report UCLA-438, University 
of California, Los Angeles, Sept. 14, 1960. 

5. J. P. Friend, H. W. Feely, P. W. Krey, J. Spar, and A. Walton, The High Altitude 
Sampling Program, Report DASA-1300 (Vols. 1, 2A, 2B, 3, 4, and 5), Defense Atomic- 
Support Agency, Aug. 31, 1961. 

6. C. F. Miller, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcan 
Irazu (Costa Rica) by Plants and People, Parts Two and Three, SRI Project IMU-4890, 
Stanford Research Institute, 1967. 

7. National Academy of Sciences— National Research Council, Damage to Livestock from 
Radioactive Fallout in Event of Nuclear War, Publication No. 1078, Washington, D. C, 
1963. 

8. National Committee on Radiation Protection and Measurements, Exposure to Radiation 
in an Emergency, Report No. 29, 1962. 

9. J. L. Mackin, S. L. Brown, and W. B. Lane, Beta Radiation Dosimetry for Fallout 
Exposure Estimates: Comparison of Theory and Experiment, SRI Project 7402, 
Stanford Research Institute, 1969. 



106 MILLER 

10. S. L. Brown, Disintegration Rate Multipliers in Beta-Emitter Dose Calculations, SRI 
Project IMU-5116, Stanford Research Institute, 1965. 

11. J. D. Teresi and C. L. Newcombe, An Estimate of the Effects of Fallout Beta Radiation 
on Insects and Associated Invertebrates, Report AD-63 3024, Naval Radiological Defense 
Laboratory, Feb. 28. 1966. 

12. Report of ICRP Committee on Permissible Dose for Internal Radiation (1959), J. Health 
Phys., 3 (1960). 

13. J. L. Kulp and A. R. Schulert, Strontium-90 in Man and His Environment, USAEC 
Report NYO-9934 (Vols. I, II, and III), Columbia University, 1961 and 1962; also R. S. 
Hirshman and A. R. Schulert, Strontium-90 Assay of Various Environmental Materials, 
USAEC Report NYO-9934(Vol. Ill) Ext., Columbia University, 1961. 

14. C. F. Miller and S. L. Brown, Models for Estimating the Absorbed Dose from 
Assimilation of Radionuclides in Body Organs of Humans, SRI Project IMU-4021, 
Stanford Research Institute, 1963. 

15. C. F. Miller, Assessment of Nuclear Weapon Requirements for Assured Destruction, 
URSRC Report 757-6. URS Research Company, 1970. 

16. R. K. Laurino, National Entity Survival Following Nuclear Attack, SRI Project 
IN-OAP-28, Stanford Research Institute, 1967. 

17. William Beecher, Soviet Arms Gain Detected by U. S., New York Times, 1969. 

18. Ashley W. Oughterson and Shields Warren, Medical Effects of the Atomic Bomb in 
Japan, Division VIII. Vol. 8, National Nuclear Energy Series, McGraw-Hill Book 
Company, Inc., New York, 1956. 

19. Raisuke Sirake, Medical Survey of Atomic Bomb Casualties, Research on the Effects and 
Influences of the Nuclear Bomb Test Explosives, Volume II, Japan Society for the 
Promotion of Science, Tokyo, 1956. 

20. C. F. Miller, Protection of People by Structures from the Initial Radiation, Blast, and 
Thermal Phenomena of Nuclear Explosives, Research Report No. 7, Office of Civil 
Defense, Department of Defense, 1962. 



PREPARATION AND USE OF FALLOUT 
SIMULANTS IN BIOLOGICAL EXPERIMENTS 



WILLIAM B. LANE 

Stanford Research Institute, Menlo Park, California 



ABSTRACT 

Facilities developed by the Office of Civil Defense for the production of synthetic fallout 
are described. The capability for simulating nuclear fallout is reported and is exemplified by 
a description of the production (1) of a 300-lb batch of synthetic fallout tagged with 15 Ci 
of ' Cs and (2) a small routine batch of synthetic fallout tagged with Y, which is 
produced once or twice a month. 



The nuclear weapons test-ban treaty, which effectively prohibits the detonation 
of nuclear weapons in the atmosphere, has made necessary the development of 
alternative experimental techniques for obtaining data on the interaction of 
radioactive fallout with the environment. Procedures for preparing synthetic 
fallout that simulates some of the important properties of fallout generated by 
nuclear weapons have been developed over the past few years. Synthetic 
radioactive fallout can be employed in many experimental programs directed 
toward obtaining operational and technical data used to develop plans for 
survival and recovery measures during and after a nuclear war. 

Procedures developed to simulate many properties of real fallout 1 3 have 
been used in the hot-cell facility at Camp Parks to prepare batches of synthetic 
fallout for studies sponsored by the Office of Civil Defense. Investigators at the 
U. S. Naval Radiological Defense Laboratory (USNRDL), Cornell University, 
Oak Ridge National Laboratory (ORNL), University of Tennessee, University of 
California, Lawrence Radiation Laboratory, Colorado State University, Uni- 
versity of North Carolina, and Stanford Research Institute all have used 
synthetic fallout prepared to their specifications. 

Stanford Research Institute now operates the Camp Parks hot cell for the 
Office of Civil Defense. 



107 



108 LANE 

SYNTHETIC-FALLOUT PRODUCTION PROCESS 

The steps in producing synthetic fallout include: (1) mineral processing to 
produce sized particles in ton quantities, (2) radioisotope processing in the hot 
cells, (3) radiotaggmg the mineral particles in concrete mixers and high- 
temperature furnaces, and (4) testing and control to ensure the radiochemical, 
chemical, and physical properties of the synthetic fallout. 

Mineral Processing 

Radioactive particles from 44 to 700 /i in diameter comprise a very large 
fraction of local fallout from a land-surface nuclear detonation. Four particle- 
size groups — 44 to 88, 88 to 175, 175 to 350, and 350 to 700 [d — are produced 
to cover the range. 

Carload lots of feldspar, quartz, and clay, the principal minerals in the 
earth's crust, were purchased. Some required crushing and pulverizing, but most 
were in the form of sand and required only sieving to produce the full range of 
particle sizes. 

The particles were separated into sized groups on a commercial sieving 
machine manufactured bv Novo Corp. A wet centrifugal method was used to 
remove fine particles from the 44- to SS-[i material. Sieving efficiency was 
measured and controlled by frequent determinations of particle size made with 
Tyler sieves and a Ro-Tap machine. Each of the size groups was produced in ton 
quantities and stored in color-coded bags and barrels. If extremely clean cuts 
were required, pound lots of these stored particles were further processed on the 
Ro-Tap bv wet sieving. 

Some important phvsical properties of the four particle-size groups of 
Wedron sand were measured by careful sieving into a large number of 
intermediate sizes. The data permitted calculations of the properties as shown in 
Table 1. 



Table 1 
PHYSICAL PROPERTIES OF WEDRON SAND 





Number of 


Average surface 


Average particle 


Group, 


particles 


area per particle, 


diameter, 


M 


per gram 


cm 


M 


44 to 88 


6.98 x 10 6 


6.69 x 10" ? 


47 


88 to 175 


6.20 x 10 5 


3.21 x 10 4 


101 


175 to 350 


7.54 x 10 4 


1.39 x 10 3 


210 


350 to 750 


7.09 x 10" 


7.85 x 10 3 


500 



FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS 



109 



Radioisotope Processing 

Two hot cells are provided for radioisotope handling. Each cell has an inside 
floor area 8 by 8 ft. Shielding is provided by 2-ft-thick concrete walls, and there 
is a 2-ft-thick zinc bromide-filled viewing window. 4 One cell is fitted with a pair 
of model 8 Hevi-Duty Master-Slave manipulators and the other cell with a pair of 
model 4 manipulators. Ventilation is provided by blowers that maintain a slight 
negative pressure inside the cells. Leakage air, amounting to about 500 cfm, is 
exhausted through absolute filter banks. A V 2 -ton monorail hoist provides access 
to the cells and to a shielded alleyway. One cell is equipped with a V 4 -ton jib 
crane that remains inside the enclosure. Each cell has through-wall holes for 
sample removal and for pressure, vacuum, and water lines. Each cell is supplied 
with a 100-amp three-phase four-wire electrical service. Work tables consist of 
stainless-steel trays atop cubic-yard concrete blocks that are carried on 
warehouse dollies. A 15 -gal drum is cast into the center of the concrete block to 
serve as a receptacle for waste disposal. Separate work tables set up for specific 
operations are wheeled into the hot cell as needed. 

Solid waste is collected in polyethylene-lined drums and then transferred to 
approved shipping boxes. Liquid waste is poured into 5-gal polyethylene carboys 
and then solidified with Micro-Cell E(a Johns-Manville product). Ultimate 
disposal is contracted to a licensed company such as Nuclear Engineering of 
Walnut Creek, Calif. 



40 



Ba, 

Ru, 



1 40 



La, 
Ru, 



Radioisotopes that have been processed include kilocuries of 
147 Pm, and 204 T1; multicuries of 85 Sr, 90 Sr, 95 Zr, 95 Nb, » 
I31 I, 137 Cs, 144 Ce, ,77 Lu, and l 9 8 Au; millicuries of 8 5 Rb and ' 34 Cs; and 
gross fission product. 

Many of these radioisotopes have been produced by neutron irradiation in 
the nearby General Electric Company test reactor at Vallecitos. Tools and 
equipment for encapsulating, testing, and opening the irradiated capsules are 
available in the hot cells. 



Radiotagging Mineral Particles 

Radiotagging consists in spraying a weak acid solution of a selected 
radioisotope on a charge of mineral particles as they are tumbling in a rotating 
mixer. The particles are then dried by the direct application of heat or by 
introduction of heated air to the mixer. Subsequent treatment determines the 
solubility or availability of the radioisotope. 

A nonleaching synthetic fallout is produced by "fixing" the radioisotope 
with an overcoat of sodium silicate. This is accomplished by spraying a solution 
of sodium silicate on the dry radiotagged particles while they are still in the 
mixer; after this spraying they are again dried. The amount of sodium silicate is 
adjusted to produce a layer less than 1 ju thick. Tagged particles are then 
removed from the mixer and placed in a furnace at 2000°F to fuse the sodium 



110 LANE 

silicate layer and seal in the radionuclide. The physical properties of the mineral 
particles are not appreciably altered by this treatment. However, in many cases a 
realistic and specified solubility of the radionuclide is desired. This is 
accomplished by heating the radiotagged mineral particles (without sodium 
silicate) to previously determined temperatures that alter the particle surface and 
control the combined chemisorption and diffusion of the radionuclide in the 
particle matrix. 

The batch size of mineral particles dictates which of the available rotating 
mixers is selected for a particular operation. Ball mills and twin-shell blenders are 
used for gram and pound lots. Portable 1-cu-ft concrete mixers are used for lots 
of up to 100 lb. Specially modified 2-yd concrete mixers are used for 500Tb 
batches. The latter are charged with mineral particles by lift truck and hoppers. 
The radioisotope is sprayed on, the particles are dried, the sodium silicate is 
sprayed on, and the particles are dried again; the synthetic fallout is then 
discharged on an endless belt that conveys it to a bucket elevator and a metering 
hopper where it is placed in stainless-steel pans. The pans are pushed by 
hydraulic ram along skid rails into a gas-fired furnace. After spending an hour in 
the furnace at 2000°F, the pans are pushed out the other end of the furnace 
where the synthetic fallout cools. Further pushing automatically dumps the pans 
and discharges the cooled synthetic fallout on to another endless belt for 
transfer to shielded hoppers. All these operations are performed from a remote 
and shielded location to minimize the radiation dose to personnel. 

Several electric furnaces are available for heating gram and pound lots of 
synthetic fallout. A large number of lead and concrete containers are available to 
meet a wide range of volume and shielding requirements. 

Testing and Control of Synthetic Fallout 

Radiation-measuring equipment for analytical purposes consists of a 4-pi 
ionization chamber, a gamma spectrometer, a scintillation crystal counter, and a 
Geiger counter. 

l.The 4-pi ionization chamber is used to assay all incoming shipments of 
radioisotopes and all outgoing batches of synthetic fallout. Over the years it has 
proved to be a reliable instrument, and the results obtained with it are 
considered very accurate. 

The 4-pi ionization chamber is filled with argon to 600 psig at 70 F. The 
cylindrical steel chamber is 1 1 in. in diameter and 14 in. high and has a reentrant 
sample thimble 1% in. in internal diameter by 12 in. deep. The entire chamber is 
shielded by 3 in. of lead. Current produced in the chamber by ionizing radiation 
is applied to suitable load resistors; the resulting voltage drop drives a 
plate-difference amplifier and is read out on a microammeter. The useful 
ionization current ranges between 4 X 10" 1 ° and 3 X 10" 5 ma. All readings are 
normalized to a standard response of 5.60 X 10 " 7 ma for 100 jKg of radium. The 



FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS 111 

response (milliamperes per disintegration per second) of many radioisotopes has 
been accurately determined. 

2. The gamma spectrometer is used to verify the radiochemical purity of all 
incoming radioisotopes and all outgoing batches of synthetic fallout. It is 
composed of a pulse-height analyzer, a paper-tape printer, and an X— Y plotter. 
The Technical Measurement Corp. (TMC) Gammascope analyzes signals whose 
pulse height is proportional to photon energy and sorts the signals into one of 
100 channels, depending on their peak amplitude. The accumulated data are 
presented on a display oscilloscope and then read out on a TMC paper-tape 
printer or a Moseley X— Y plotter. 

3. The scintillation counter consists of a 3- by 3-in. sodium iodide crystal 
with a l'/ 4 - by 2-in. deep well mounted on an E&M Instruments Co., Inc., 3-in. 
photomultiplier tube whose output is fed directly into a Systron model 1091-3 
scaler. The scaler is controlled by a Nuclear Dual Timer. A John Fluke 
Manufacturing Company, Inc., model 412A high-voltage power supply provides 
dynode string voltage for the photomultiplier tube. Shielding consists of a lead 
cylinder 3 in. thick, 9 in. in internal diameter, and 22 in. high. A 2-in. -thick lead 
cover moves in and out to permit sample access to the well crystal. 

4. A Geiger counter consisting of a thin-walled Geiger tube and a Berkeley 
scaler measures activity on filter papers that are used to collect air samples or to 
swipe floors or bench tops. 

Instruments for radiation safety and contamination control consist of 1-cfm 
constant-flow air samplers, El-Tronics, Inc., CP30 meters (Cutie Pie), and 
Nuclear Electronics XX2 survey instruments. 



SYNTHETIC-FALLOUT PRODUCTION 

Synthetic-fallout production can be illustrated and the capability exem- 
plified by reporting on two production batches. 

Cesium-137 Tagged Synthetic Fallout 

Investigators at ORNL requested a synthetic fallout for an ecological study 
they were conducting for the Office of Civil Defense. The study measured 
effects of l 37 Cs on a controlled ecological system over a period of years. 

Three hundred pounds of 88- to 175-/J sand was tagged with I37 Cs in a 
1-cu-ft mixer in two batches. The first batch of 140 lb had a specific activity of 

36.6 mCi/lb, and the other batch of 160 lb had a specific activity of 

46.7 mCi/lb. All the tagged sand was heated to 900°C and held at that 
temperature for 2 hr. The resulting synthetic fallout was leached overnight by 
0.1N HC1. Overnight leaching of 2-g samples of the resulting synthetic fallout by 



112 LANE 

Since the ORNL study was designed to continue for several vears, leaching 
data covering a few hours seemed inadequate to predict the availability of 
cesium. Accordingly, long-term tests were initiated to measure the leaching of 
cesium at extreme dilutions. This was accomplished by setting aside the 20-ml 
aliquot of 0.1N HC1 that resulted from overnight leaching and adding a second, 
similar aliquot to the once-leached synthetic fallout. This process of leaching the 
same mineral fraction for random time intervals with fresh aliquots was 
continued for 1250 days and resulted in the accumulation of 28 successive 
leaching aliquots. 

The mechanism for the first 10 days of leaching appeared to be a 
chemisorption process that was well described by a Freundlich adsorption 
equation of the form 

C m =kC? (1) 

where C m is the average cesium concentration in the mineral particles and C/ is 
the concentration in the leaching solution. 

It appeared that the longer-term leaching behavior (from 10 days to more 
than 3 years) was described by a diffusion-limiting mechanism corresponding to 
the solution of Frick's law for diffusion from a sphere: 



: 7T 2 Zj 2 



^p = 



When t is sufficiently large, the first term of the series is a good approximation, 
so that 



?-* •*(-;) 



(3) 



where 



C = initial average cesium concentration in the mineral 
C m = concentration after various leaching times 
t = time of leaching 
r = radius of the fallout particle 
D = diffusion coefficient 

In this approach the leaching of radionuclides from fallout particles for long 
periods of time can be predicted if the numerical values of k, n, and D in Eqs. 1 
and 2 are known. 



FALLOUT SIMULANTS IN BIOLOGICAL EXPERIMENTS 113 

Monthly Batch of Multicurie 90 Y Tagged Synthetic Fallout 

A 250-mCi Sr "cow" was started in a lead-shielded Berkeley glove box 
about 3 years ago to supply Y for a study of beta effects on beans. To satisfy 
requirements for several OCD studies, the activity level was soon raised to 30 Ci. 
This was accomplished by wheeling the shielded box inside one of the two hot 
cells to ensure double containment and simply adding 30 Ci of carrier-free 90 Sr 
to the 400-ml beaker that already contained 250 mCi and 2 g of inactive 
strontium nitrate. 

Yttrium-90 is "milked" from the equilibrium mixture by taking the dry 
strontium nitrate up in 25 ml of distilled water. Strontium nitrate is then 
precipitated by adding 125 ml of 90% nitric acid. The acid solution containing 
the 9 Y is removed through a filter frit by suction and transferred to the second 
hot cell where it is evaporated to dryness. The carrier-free Y is taken up in 
25 ml of water, and 2 g of inactive strontium nitrate is added and precipitated 
with 125 ml of 90% nitric acid. The acid solution of Y is again filtered off, 
evaporated to dryness, and taken up in 100 ml of 0.1.Y HN0 3 . About 20 Ci of 
90 Y are usually available at this point. A iOO-jll] aliquot of this solution is 

assayed in the 4-pi ionization chamber to determine the volume required for 
tagging the particular batch of sand. In the meantime, the Sr cow in the 
Berkeley box is slowly evaporated to dryness and taken up in 25 ml of water to 
make ready for the next milking. 

Sufficient Wedron sand to meet the batch requirements is prepared by wet 
sieving and Ro-tapping to 'ensure that all particles are within the specified size 
range. The sand (up to 600 g) is added to the rotating drum of a ball mill that is 
operating inside the second hot cell, and the calculated volume of carrier-free 
90 Y solution is sprayed on the tumbling particles. The radiotagged sand is dried 
by the heat from a hot plate placed directly under the metal drum, after which 
10 ml of sodium silicate is sprayed into the rotating drum to overcoat the 
particles. After the particles are again dried, the synthetic fallout is transferred 
to a crucible and placed in a muffle furnace at 1950 F for 1 hr. The synthetic 
fallout is removed from the furnace, cooled, and returned to the hot cell for 
assay. When it is determined that the specific activity is within acceptable limits, 
the synthetic fallout is packaged and shipped. 

The 90 Sr cow has been milked 25 times for the University of California, 22 
times for the University of Tennessee, and 13 times for studies at Stanford 
Research Institute. 



ACKNOWLEDGMENT 

This work was done by Stanford Research Institute under Office of Civil 
Defense Work Unit 321 1C. 



114 LANE 

REFERENCES 

1. William B. Lane, Fallout Simulant Development: The Sorption Reactions of Cerium, 
Cesium, Ruthenium, Strontium, and Zirconium— Niobium, Project No. MU-5068. Stan- 
ford Research Institute, November 1965. 

2. William B. Lane, Fallout Simulant Development: Temperature Effects on the Sorption 
Reactions of Cesium on Feldspar, Clay, and Quartz, Project No. MU-6014, Stanford 
Research Institute, March 1967. 

3. William B. Lane, Fallout Simulant Development: Temperature Effects on the Sorption 
Reactions of Strontium on Feldspar, Clay, and Quartz, Project No. MU-6503, Stanford 
Research Institute, March 1968. 

4. William B. Lane, Argon Improves ZnBr^ Shielding Windows, Nucleonics, 22: 88-89 
(February 1964). 

5. Carl F. Miller, Response Curves for USNRDL 4-pi Ionization Chamber, Report 
USNRDL-TR-155, Naval Radiological Defense Laboratory, May 1957. 



FATE OF FALLOUT INGESTED 
BY DAIRY COWS 



G. D. POTTER, G. M. VATTUONE, and D. R. McINTYRE 

Lawrence Radiation Laboratory, Bio-Medical Division, University of California, 

Livermore, California 



ABSTRACT 

The fate of fallout ingested by dairy cows — its retention, absorption from the gut, 
deposition in tissues, and transport to man — is of direct concern when we consider 
survival of livestock and ingestion of their by-products by man in the event of a nuclear war. 
The data presented here are from two cows fed debris from a nuclear cratering event. The 
first of these was given a single dose of debris, and the second received a daily 
administration of debris. The gamma-emitting radionuclides observed in milk were I, 

132 Te, 140 Ba, l 8 ' W, 187 W, and l88 W- 188 Re, and in urine, 74 As, 103 Ru, 131 I, l32 Te, 
181 W, 187 W, and 188 W- 188 Re. 

Maternal and fetal tissues in the second cow were analyzed for gamma-emitting 
radionuclides and compared with the maternal plasma levels of these nuclides. Maternal 
kidney, liver, and spleen concentrated As, but fetal tissues had none. Both maternal and 
fetal thyroids concentrated I by 10 5 over maternal plasma. Fetal bone was the primary 

target organ for Ba. The radiotungstens were concentrated by fetal bone and by 

maternal kidney, liver, spleen, and bone. Elimination patterns of the nonabsorbed 
radionuclides from debris are also presented. 



The fate of fallout ingested by livestock — its retention, absorption from the gut, 
deposition in tissues, elimination in urine or feces, and transport to man via meat 
and milk — is of direct concern when we consider the survival of livestock in 
the event of a nuclear war or the hazard related to ingestion of food products 
derived from contaminated livestock. Probably the most damaging effects from 
the ingestion of large amounts of fallout by animals are the early effects of 
radiation damage and their sequelae leading to radiation sickness and subsequent 
death. If livestock survive these initial insults, then their suitability as sources of 
food for man becomes important in long-range considerations. 

In recent years the only debris from actual nuclear tests which has been 
available for study has come from the Plowshare nuclear cratering program. Our 



115 



116 POTTER, VATTUONE, AND MclNTYRE 

studies are concerned primarily with the biological availability of debris 
radionuclides from a specific Plowshare nuclear cratering experiment, the 
Schooner event. This most recent Plowshare nuclear cratering experiment 
consisted of a 31-kt nuclear detonation executed on Dec. 8, 1968, at the Nevada 
Test Site. Debris from this event was administered orally to a lactating cow and 
to a near-term pregnant cow for maternal— fetal transfer studies. These 
experiments deal primarily with the distribution of gamma-emitting radio- 
nuclides in the dairy cow fed debris from this event. 



METHODS 



Debris from the base-surge area of the Schooner event was collected in 
fallout trays or in a cyclone-type separator. In both cases the debris consisted of 
fine dust particles that passed through an 88-jU sieve. One hundred ninety-two 
grams of the debris from the tray were fed to a lactating cow in \\ -oz gelatin 
veterinary capsules administered with a balling gun. The animals were 
catheterized and maintained in metabolic stalls to facilitate collection of urine 
and feces. Samples of feces, urine, and milk for each 24-hr collection period 
were pooled and mixed in order to obtain homogeneous samples for counting. 
Heparinized blood samples were taken following each morning's milking. 
Samples consisting of 200 g of each of the metabolic products were placed in 
aluminum tuna cans with formalin added as a preservative and were sealed for 
counting. 

In the second experiment, the maternal— fetal transfer study, 895 g of debris 
from the cyclone collector was divided into four equal daily doses and 
administered to a near-term pregnant cow in the same manner. Smaller tissues 
were minced and suspended in a 2% agar solution in order to ensure constant 
counting geometry. 

All samples were counted on a solid-state germanium— lithium [Ge(Li)] 
drifted detector using a 2048-channel analyzer (gain = 1.0 keV/channel). The 
high resolution of these Ge(Li) systems has made them extremely useful for the 
analysis of complex mixtures of gamma-emitting radionuclides. The resulting 
gamma-ray spectra were recorded on magnetic tape and analyzed by using a 
computer code to quantitate the area under each of the gamma peaks, which 
were then listed in order by energies. The peaks of interest for specific 
radioisotopes were then selected and processed with a second code, which 
corrected for physical decay and subsequently calculated the activity per unit 
weight, the recovery as a fraction of the administered dose for each collection, 
and the fraction of the administered dose per unit weight of each sample. In 
addition, this code also plotted the recovery of milk, urine, feces, and plasma as 
a percent of the administered dose per kilogram vs. time after administration. 



FATE OF FALLOUT INGESTED BY DAIRY COWS 



117 



RESULTS AND DISCUSSION 

Experiment I: Single Administration of Debris 

Tabic 1 shows the nuclides recovered in milk, urine, and feces of the cow 
following a single oral administration of 92 g of early (5 days postshot) 
Schooner debris from fallout trays. Arsenic, ruthenium, iodine, tellurium, 
barium, tungsten, and rhenium were recovered in milk and/or urine. Manganese, 
cobalt, yttrium, zirconium, gold, and lead were observed only in feces or were in 

Table 1 

RADIONUCLIDES IN FECES, URINE, AND MILK 
FOLLOWING ORAL ADMINISTRATION OF 
SCHOONER DEBRIS TO A LACTATING COW 



Administered dose, % 



Nuclide 



Mn 
Co 

'As 



88- 



Zr 



Ru 



1 32 



Te 
Ba 



181 



1 87 



w 



w 



196 



w- 

Au 
Pb 



La 



Re 



Feces 


Urine 


Milk 


98.99 


ND* 


ND 


109.9 


ND 


ND 


50.8 


29.9 


ND 


78.9 


ND 


ND 


71.0 


ND 


ND 


91.4 


7.06 


ND 


46.4 


35.9 


2.23 


87.4 


1.28 


0.07 


93.4 


ND 


0.05 


60.1 


9.6 


0.31 


82.4 


8.8 


0.18 


80.4 


34.8 


0.43 


97.6 


ND 


ND 


96.4 


ND 


ND 



*The abbreviation ND, no data, indicates 
amounts too low for quantitation. 



levels too low to quantitate in milk or urine. The total amounts of individual 
radionuclides in the debris were relatively low compared with those of the 
radiotungstens, which were at least two to three orders of magnitude greater 
than any of the other radionuclides present. Although 196 Au was not observed 
in milk or urine, it was observed in plasma. The recovery of 188 W was greater 
than 100%. This anomaly is due to the fact that the 155-keV peak of 188 Re was 
used to measure the 188 W. The 188 Re (T^ = 16.8 hr), the daughter of 188 W 
(Ty 2 = 69 days), was in equilibrium in the debris at the time of administration, 
and, since the samples were counted shortly after collection, both the 188 Re in 
the debris and the 188 Re derived from 188 W are present in them. Rhenium is 



118 



POTTER, VATTUONE, AND MclNTYRE 



very rapidly absorbed from the gut, probably directly in the rumen, and is very 
rapidly excreted, especially in urine and milk, as observed in single isotope 
experiments. Therefore, since the first two collections of urine and milk reflect 
rhenium absorption and excretion in addition to the 188 W absorption and 
excretion, a high recovery results. 

Figure 1 shows a typical fecal excretion curve for a nonabsorbed nuclide, 
' Y. Figure 2 shows the curves for a readily absorbed nuclide, 1 I, in feces, 
urine, milk, and plasma. The curves for urinary and fecal excretion of l 3 1 1 are 
quite similar. The levels in milk initially exceed those in plasma but fall more 




60 80 100 

HOURS POSTADMINISTRATION 



Fig. 1 Typical fecal excretion curve for a nonabsorbed radionuclide ( Y) 
following a single oral administration of Schooner debris. Concentrations in 
milk, urine, and plasma are too low for quantitation or are not detected. Fecal 



. M 38 Yi 95 Zr _9S Nb? l03 RUi llOm^ ^ B a- 1HU La, "^ C e, 



57, 



Ta, 



196 



Au, and 



203 



Pb were almost identical. 



FATE OF FALLOUT INGESTED BY DAIRY COWS 



119 




60 80 100 

HOURS POSTADMINISTRATION 



20 



Fig. 2 Uptake and disappearance curves for I in feces (F), urine (U), milk 

(M), and plasma (P) following a single oral administration of Schooner debris. 



rapidly since inorganic iodine is secreted in milk, whereas the plasma level 
reflects, in addition, the presence of organic or protein-bound iodine as well as 
recycled iodine. 

Experiment II: Repeated Administration of Debris and Maternal-Fetal Transfer 

A near-term pregnant cow was fed 895 g of Schooner debris from the 
cyclone collector. This debris, recovered 6 weeks after the detonation, consisted 
of particles less than 88 jU, the bulk of which were between 20 and 50 /J. The 
debris was administered in four equal daily doses. The procedure was the same as 



120 



POTTER, VATTUONE, AND MclNTYRE 



in the previous experiment except that at 144 hr the cow was anesthetized and 
exsanguinated and maternal and fetal tissues were removed for counting. 

Figure 3 shows the fecal excretion curve for 88 Y, which is typical of nuclides 
that were not appreciablv absorbed from the gut. These included ?4 Mn, = 7 Co, 

88 Y) 89 Zr 103 Ru 110m Ag ^0 Ba _140 La 141 Ce) 182 Taand 196 Au 



10 



10° - 



1CT 1 





1 1 1 1 1 


.F 


1 1 1 


1 j 
— F 


1 




F 










- 


F 

DAILY 




1 1 1 


1 1 




/ 1 


ADMINISTRATION 

1 1 1 1 1 


1 



20 40 60 80 100 

HOURS POSTADMINISTRATION 



! 20 



140 



Fig. 3 Typical fecal excretion curve for a nonabsorbed radionuclide ( 88 Y) 
following repeated daily doses of Schooner debris. 



On the other hand, curves for nuclides that are readily absorbed differ in 
that part of the activity is recovered in milk and or urine (See Fig. 4). Examples 

88 Re, and 184 Re. Of these, 



74 



of these nuclides are As, 



1 3 1 



W. 188 \V- 



As was not observed in milk and s Re was not observed in feces; similar 
results were obtained in our studies of cows given single carrier-free isotope 



FATE OF FALLOUT INGESTED BY DAIRY COWS 



121 



10 1 



i i r 




40 60 80 100 120 

HOURS POSTADMINISTRATION 

Fig. 4 Uptake curves for ' 81 W in feces (F), urine (U), milk (M), and plasma 
(P) following repeated daily doses of Schooner debris. Curves for 185 W and 
188 W were almost identical with the exception of 188 W mentioned in the 
text. 



140 



solutions, except that 0.1% of the administered dose of 74 As was present in milk 
and 1.1% of the 186 Re was found in feces. Since the levels of radioactivity of 
the various isotopes in the debris were at least two to three orders of magnitude 
lower than those of the tungstens, some radionuclides would be expected to be 
present at or below the limits of detection. 

Table 2 shows the tissue-to-maternal-plasma (T/P) ratios, in which fetal 
tissues are considered to be organs of the maternal organism. At the time the 
debris was fed, most of the shorter-lived nuclides had decayed. Those observed 
in tissue were 74 As, 131 I, 140 Ba— 140 La, and the tungstens. Debris radio- 
nuclides not observed in tissues were omitted from the table. In maternal tissues 



122 POTTER, VATTUONE, AND MclNTYRE 



Table 2 

TISSUE-TO-MATERNAL-PLASMA RATIOS* OF MATERNAL AND FETAL TISSUES 
FROM A PREGNANT COW FED DEBRIS FROM PLOWSHARE NUCLEAR TEST 



Tissue 


74 As 


1 3 1 j 


140 Ba 


181 W 


185 W 


1 88yy 1 8^Re 


Maternal spleen 


9.8 


NDt 


2.25 


3.4 


3.0 


3.3 


Fetal spleen 


ND 


ND 


5.25 


0.18 


ND 


0.23 


Maternal kidney 


45.7 


1.25 


1.25 


9.1 


8.9 


9.37 


Fetal kidney 


ND 


1.85 


ND 


0.38 


ND 


0.27 


Maternal plasma 


1.0 


1.0 


1.0 


1.0 


1.0 


1.0 


Fetal plasma 


ND 


5.04 


3.25 


0.24 


ND 


0.20 


Maternal muscle 


6.5 


ND 


2.25 


0.16 


ND 


0.13 


Fetal muscle 


ND 


0.14 


0.62 


0.09 


ND 


0.09 


Maternal heart 


3.7 


4.56 


ND 


0.36 


0.35 


0.38 


Fetal heart 


ND 


1.39 


ND 


0.18 


ND 


0.11 


Maternal thyroid 


ND 


1.6 x 10 5 


ND 


1.90 


ND 


1.30 


Fetal thyroid 


ND 


1.8 x 10 5 


ND 


1.60 


ND 


1.20 


Maternal liver 


11.8 


0.93 


ND 


4.54 


4.16 


4.36 


Fetal liver 


ND 


1.7 3 


ND 


1.29 


1.58 


0.43 


Maternal RBC 


3.0 


0.53 


ND 


0.47 


0.41 


0.43 


Fetal RBC 


ND 


0.81 


ND 


0.11 


ND 


ND 


Maternal bone 


ND 


ND 


ND 


2.80 


3.00 


3.00 


Fetal bone 


ND 


0.80 


7.75 


5.00 


5.90 


5.60 


Maternal cerebellum 


ND 


ND 


ND 


0.11 


ND 


0.11 


Fetal brain 


ND 


ND 


ND 


0.60 


ND 


0.17 


Maternal cerebrum 


3.0 


ND 


ND 


0.09 


ND 


0.09 


Maternal bone marrow 


ND 


ND 


ND 


0.36 


ND 


0.20 


Maternal salivary gland 


7.2 


ND 


ND 


0.63 


ND 


0.56 


Maternal omental fat 


ND 


ND 


ND 


0.12 


ND 


0.12 


Maternal mammary gland 


2.8 


2.30 


ND 


1.38 


1.32 


1.29 


Maternal placenta 


5.4 


2.10 


ND 


1.25 


1.46 


1.33 


Fetal amniotic fluid 


5.3 


0.49 


0.75 


1.01 


0.96 


1.04 


Fetal thymus 


ND 


ND 


5.90 


0.10 


ND 


ND 


Fetal lung 


ND 


ND 


3.90 


0.12 


ND 


0.10 


Fetal skin 


ND 


1.78 


0.92 


0.20 


ND 


0.20 



*The tissue-to-maternal-plasma ratio = (cpm/100 g tissue)/(cpm/100 g maternal plasma). 
tThe abbreviation ND, no data, indicates amounts too low for quantitation. 



FATE OF FALLOUT INGESTED BY DAIRY COWS 



123 



the ratios of As were generally greater than unity in kidnev, liver, spleen, 
salivary gland, and musele (listed in decreasing order of concentration): 



As 

was not observed in fetal tissues. It is also of interest that, although relatively 
large amounts of As were observed in the maternal urine, it was not observed 
in milk. 

The 131 I was low at this time (7 weeks postshot), but large amounts were 
concentrated both in the maternal and the fetal thyroids. The T/P ratios for 

Ba were greater than unity in fetal plasma, spleen, thymus, and lung as well 
as in maternal spleen, kidney, and muscle. The T/P ratios for radiotungsten 
( 181 W, 185 W, and 188 W- 188 Re) were essentially the same for each tissue; this 
indicates that all the tungsten isotopes behaved similarly. The 1 8 1 W was 
determined by counting its X rays with an Nal counter at a later time, the l 8 5 W 
by measuring its 125-keV peak from the Ge(Li) spectrum, and the W by 

measuring the 15 5-keV peak of the newly formed 188 Re after that originally 
present had decayed. Maternal kidney, liver, thyroid, and bone had T/P ratios 
greater than 1. Fetal bone had a T/P ratio almost twice that of maternal bone; 
this indicates that bone is a principal target organ for radiotungsten in the fetus. 
A comparison of tungsten levels in fetal tissues generally shows that the placenta 
acts as a partial barrier to tungsten. However, tungsten that does cross the 
placenta is concentrated primarily in the developing bone. 

Despite such obvious sources of variation as differences in physical and 
chemical form in which radionuclides might exist in debris, inherent errors in 
counting statistics, and disparity of radionuclide concentrations in debris, a 
comparison of data from cows fed debris from different Plowshare experiments 
as well as carrier-free radionuclides shows excellent correlation. Transport of ions 
across the gut depends on many predictable factors; these include surface or 
mass distribution of radionuclides within fallout particles, their solubility product 
in the gut contents at different hydrogen ion concentrations (e.g., the formation 
of insoluble precipitates), and the binding of specific ion species to insoluble gut 
contents such as lignins or cellulose residues. Within single-debris experiments 
fecal elimination curves expressed as percentages of the administered dose per 
unit weight are essentially identical for the nonabsorbed radionuclides. This 
appears to demonstrate that the fecal elimination of debris radionuclides 
associated with particles less than 88 jJt depends primarily on the rate of passage 
of digesta through the gut. Many of the nuclides in debris fall in this category 
(e.g., 54 Mn, 58 Co, 60 Co, 89 Zr, ! 4 l Ce, etc.). On the other hand, a number of 
radionuclides are absorbed to varying degrees, and each of these have unique 
transfer coefficients to specific organs as metabolic pools. Examples of these 
include the iodines, arsenic, the tungstens, molybdenum, rhenium, sodium, and 
tritium. This group requires more-detailed studies. The data from such studies 
are necessary as input for the construction of predictive models such as those 
presented by Ng (this volume). 



124 POTTER, VATTUONE, AND MclNTYRE 

SUMMARY 

We have presented data on the fate of gamma-emitting radionuclides in 
debris from the Schooner event administered orallv to lactating cows. Nuclides 
appearing m milk were 131 L l 3 2 Te, 140 Ba, 181 W, 187 W, and 188 W- 188 Re, 
and those appearing in urine were 74 As, 1 03 Ru, [ 3 l I, l 32 Te, 1 8 ! W, ! 8 7 W, and 

W— Re. Levels of the other nuclides were too low for quantitation in 
biological products. At the time the maternal—fetal transport experiment was 
carried out, only 74 As. 131 I, 140 Ba, 181 W, 185 W, and ^8 w _i88 Re wer£ 
present in adequate amounts for quantitation. The 74 As did not appear to cross 
the placenta. The concentration of I was similar in both the maternal and 

fetal thyroid glands. Fetal bone and spleen concentrated ] Ba. Bone appeared 
to be the primary target organ for tungstens in the fetus. Transfer coefficients 
derived from such experimental data can be used for predicting milk and meat 
contamination and internal organ burdens. 

ACKNOWLEDGMENT 

This work was performed under the auspices of the U. S. Atomic Energy 
Commission. 



FATE OF FALLOUT INGESTED BY SWINE 
AND BEAGLES 



ROBERT J. CHERTOK and SUZANNE LAKE 

Lawrence Radiation Laboratory, Bio-Medical Division, LJniversity of California, 

Livermore, California 



ABSTRACT 

The increased use of nuclear energy necessitates thorough investigation of the biological 
availability of radionuclides released to the biosphere. The radionuclides produced by a 
nuclear event occur in a variety of chemical and physical forms and are associated with 
particles of various sizes. Therefore distribution or retention data from laboratory 
experiments with a single, pure radionuclide cannot reasonably be extrapolated to a 
radionuclide in a complex mixture, as in debris. The Plowshare nuclear cratering 
experiments offer a unique opportunity to study the biological availability of radionuclides 
associated with debris from nuclear detonations. 

We have taken advantage of these events to determine the retention and excretion of the 
gamma-emitting radionuclides produced by three Plowshare detonations and one other 
event. Near-surface atmospheric debris was administered orally to the experimental animals 
(two for each study), which were then confined to metabolic cages for the duration of the 
experiment (5 to 9 days). For two events the experimental animals were beagles, and for 
two others they were peccaries {Tayassu tajacu). Daily whole-body analyses were performed 
with a lithium-drifted germanium [Ge(Li)] detector. Daily collections of urine and feces 
were analyzed similarly on the same detector. 

In these studies the percentage of dose absorbed is the sum of the percentage excreted in 
the urine and the percentage remaining in the whole body at the conclusion of the 
experiment. Our results indicate that for some radionuclides the percentage absorbed varies 
not only from literature values but also from event to event. Admittedly these variations 
may be due to species differences, but they are more likely due to variations in the chemical 
and/or physical form of the radionuclide in the debris of different events. For the 
radionuclides analyzed so far, ranges of absorption for the four events are ~ Mn, 1.0%; 
58 Co, 4.3%; 74 As, 45.4%; 88 Y, 1.1%; 99 Mo, 11.5 to 31.0%; 103 Ru, not detectable (ND) to 
5.5%; 122 Sb. 4.0 to 4.2%; 131 I, 32.7 to 78.5%; I32 Te, 0.9 to 24.5%; 140 Ba- 14 °La, 0.5 to 



4.1%; 141 Ce, ND to 0.5% 



188 Re, 18.2%; and 198 Au, 4.1 to 



W, 7.0 to 41.4%; W 

7.7% (the radionuclides for which only one value is given were measured in only one event) 



The increased use of nuclear energy necessitates investigation of the fate of 
radionuclides released to the biosphere. The radionuclides produced by atomic 



125 



126 CHERTOK AND LAKE 

explosions occur in a variety of chemical and physical forms and are associated 
with particles of various sizes. Thus the radionuclides in debris usually differ in 
biological activity from the simple forms encountered in laboratory experiments. 

In the nuclear cratering excavations carried out as part of the Plowshare 
Program for the study of peaceful uses of atomic energy, we have a unique 
opportunity to study the biological availability of the radionuclides in the 
atmospheric debris produced by an atomic detonation. We are therefore 
conducting as many experiments as possible in conjunction with these events to 
accumulate enough information to develop predictive capability in terms of the 
absorption and excretion rates of radionuclides produced bv different kinds of 
nuclear events and to furnish input for models that predict the biological impact 
of radioactive fallout. 

To date we have studied four events, of which all but the first were 
Plowshare tests. In these experiments atmospheric debris was collected at 10(30 
to 4000 ft from the sites of detonation, weighed, and placed in gelatin capsules. 
These were then orally administered to the experimental animals (two animals 
per experiment). The animals used in Events I and II were beagles; those in 
Events III and IV were peccaries {Tayassu tajacu). The peccary, a wild pig native 
to the southwestern United States, was chosen as an experimental animal 
because its small size is an advantage in whole-body counting and because its 
physiology closely resembles that of man. The animals were confined in 
metabolic cages for the duration of the experiment and were analyzed daily for 
the gamma-emitting radionuclides by whole-body counting with a solid-state 
germanium (lithium-drifted) detector and a 2048-channel pulse-height analyzer. 
Daily urine and feces samples were collected, preserved with formaldehyde, 
sealed in tuna cans of approximately 200 cc capacity, and analyzed for the 
gamma-emitting radionuclides on the same detector. This procedure was 
followed until the excreta and whole-body activities reached very low levels, 
between 5 and 9 days. 

All the radionuclides discussed in this report are listed in Table 1 under each 
event, along with the percentages retained in the whole bodv and recovered in 
the urine and feces. The table also includes the values listed by the International 
Commission on Radiological Protection (ICRP) 1 for the fraction transferred 
from the gastrointestinal tract to blood. All values are corrected for physical 
decay. The values for radionuclide absorption used in this presentation represent 
the sum of the radionuclides excreted in the urine and those remaining in the 
whole body at the termination of the experiment. Of course, this restricted 
definition omits consideration of any portions absorbed and excreted by other 
routes (e.g.. excreted in bile) or portions completely unabsorbed and still 
remaining in the lumen of the gastrointestinal tract. 

For the first radionuclide listed, 54 Mn, the absorption (whole- 
body + urinary excretion) was 1.0% of the dose. The ICRP value is listed as 
10.0%. However, Furchner et al. demonstrated that ^ Mn was poorly absorbed 



FALLOUT INGESTED BY SWINE AND BEAGLES 



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128 CHERTOK AND LAKE 

from the gut of mice, rats, monkeys, and dogs and that after oral administration 
rapid fecal excretion resulted in a whole-body retention of less than 1%. 

Heinrich and Gabbe 3 reported that inorganic 60 Co administered orally to 
rats was excreted in 2 days, 90% in the feces and 15% in the urine; that 
remaining in the body (0.9%) had a biological half-life of 18 days. Our 
experiment indicates that 4.3% of the dose of 58 Co was absorbed; the ICRP 
value is 30%. 

According to Schroeder and Balassa, pentavalent and trivalent arsenic differ 
markedly in their metabolism. Pentavalent arsenate, normally nontoxic, is 
rapidly excreted by the kidneys, whereas toxic trivalent arsenic is excreted 
mainly by the intestines. It seems possible that the debris of Event IV contained 
both forms since we found 45.4% of the administered dose to be absorbed; the 
ICRP value is 3%. 

For 88 Y, 1.1% of the administered dose was absorbed. The ICRP value is less 
than 0.01%. These two values are probably statistically the same. Chemically 
yttrium is closely related to the lanthanides, and, on the basis of its chemical 
properties and metabolic behavior, ' Y can be grouped with the heavy 
lanthanides. 5 According to the results of Durbin et al., 6 other heavy lanthanides 
are poorly absorbed. 

The absorption of 99 Mo ranged from 11.5 to 31.0%, compared with an 
ICRP value of 80%. Bell et al. 7 reported that in swine 79% of the orally 
administered dose was excreted in the urine and about 12% in the feces in the 
first 5 days; the rate of urinary excretion was increased when the Mo was 
diluted with carrier molybdenum. Admittedly species differences may be 
involved, but it is probable that the chemical and/or physical state of the 99 Mo 
in the debris is a major factor. The radionuclides in debris are associated with 
particles of various sizes and may be either surface distributed or volume 
distributed; both particle size and mode of distribution affect the availability of 
the nuclide for absorption from the gut. 

Van Dilla 8 found 103 Ru to be poorly absorbed by the gut in the rat. Our 
values ranged from nondetectable levels to 5.5%; the ICRP value is 3%. 

Moskalev 9 showed that about 3% of orally administered 124 Sb is absorbed 
from the gastrointestinal tract of rats. Our data for ! 22 Sb are in agreement; our 
range is from 4.0 to 4.2%. The ICRP value is 3%. 

The 131 I absorption in our experiments ranged from 32.7 to 78.5% of the 
administered dose; the ICRP value is 100%. According to the results of Busnardo 
and Cassan, 10 however, iodine from the body pool is excreted in part in the 
feces. This may account somewhat for our lower absorption values, but it is 
probable that the chemical— physical state of the ] I was a major factor. 

Wright and Bell 1 1 found that, in swine given a single oral dose of l Te, over 
70% was excreted in the feces and approximately 20% in the urine within 
120 hr. Moskalev 9 reported similar values in rats; 10 to 25% of orally 
administered ' 27 Te was absorbed. Our range of absorption for 1 32 Te was from 
0.9 to 24.5% of the dose; the ICRP value is 25%. 



FALLOUT INGESTED BY SWINE AND BEAGLES 129 

The isotopes of lanthanum are not absorbed through the intestinal wall to a 
significant degree, 6 but 140 Ba is absorbed. 12 The major part of an equilibrium 
mixture of l °Ba- 1 La injected intraperitoneally in rats was eliminated in the 
feces; 12 the kidney appeared to differentiate between l °Baand l ° La and to 
retain 1 La. In our experiments the animals were fed an equilibrium mixture of 
the two radionuclides, and the nuclide measured was ! La. Our results indicate 
an absorption range from 0.5 to 4.1% of the dose. The ICRP values are 5% for 
barium and less than 0.01% for lanthanum. 

It has also been shown that 1 Ce, too, is poorly absorbed by the gut in 
rats. 8 Our values for ] 4 l Ce indicate a range from nondetectable amounts to 
0.5% of the dose. The ICRP value is less than 0.01%. Considering the difficulties 
in measuring such small quantities of l l Ce and the counting statistics, the 
values are probably statistically the same. 

Kaye 1 3 has reported that a total of approximately 44% of the orally 
administered dose of l 8 5 W and l 8 7 W was excreted in the urine of rats. Our data 
for 187 W and 188 W- 188 Re range from 7 to 40.8%. The ICRP value is 10%. 
Other data from this laboratory indicate that 71% of the orally administered 
dose of l 8 1 W (as K 2 W0 4 ) is absorbed by beagles. 

About 15% of 1C Au administered by mouth or rectum to humans in the 
form of colloidal or salt solutions was absorbed and excreted rather rapidly. 1 
For 196 Au and Au, our range of absorption is from 4.1 to 7. 7% of the dose. 

The ICRP value is 10%. 

In summary, the differences between our data obtained with debris and the 
ICRP values can be attributed to species differences and/or the chemical- 
physical form of the radionuclides in debris. The importance of the latter 
consideration is demonstrated by our finding that absorption for the same 
radionuclides sometimes varies from event to event. 



ACKNOWLEDGMENT 

This work was performed under the auspices of the U. S. Atomic Emergy 
Commission. 



REFERENCES 

1. International Commission on Radiological Protection, Report of Committee II on 
Permissible Dose for Internal Radiation (1959), pp. 154-230, Pergamon Press, Inc., 
New York, 1960. 

2. J. E. Furchner, C. R. Richmond, and G. A. Drake, Comparative Metabolism of 
Radionuclides in Mammals. Ill, Health Pbys., 12: 1415-1423 (1966). 

3. H. C. Heinrich and E. E. Gabbe, Stoffwechselverhalten des anorganischen Kobalts und 
des in der vitamin Bi2-bzw. Vitamin Bj2 coenzyme-struktur organisch gebundenen 
Kobalts in s'a'ugetier-organismus, Z. Naturforsch., B, 19: 1032-1042 (1964). 

4. H. A. Schroeder and J. J. Balassa, Abnormal Trace Metals in Man: Arsenic, J. Cbron. 
Dis., 19: 85-106 (1966). 



130 



CHERTOK AND LAKE 



5. D. H. Copp. J. G. Hamilton, D. C. Jones, D. M. Thomson, and C. Cramer, The Effect of 
Age and Low-Phosphorus Rickets on Calcification and the Deposition of Certain 
Radioactive Metals in Bone, Transactions of the Conference on Metabolic Interrelations, 
Vol. 3, pp. 226-258, 1951. 

6. P. W. Durbin, M. H. Williams, M. Gee, R. N. Newman, and J. G. Hamilton, Metabolism 

of the Lanthanons in the Rat, Proc. Soc. Exp. Biol. Med., 91: 78-85 (1956). 

9 9 

7. M. C. Bell, B. H. Diggs, R. S. Lowry, and P. L. Wright, Comparison of Mo Metabolism 

in Swine and Cattle as Affected by Stable Molybdenum, J. Nutr., 84: 367 — 372 (1964). 

8. M. A. Van Dilla, Zinc-65 and Zirconium-95 in Food, Science, 131: 659-660 (1960). 

9. Y. I. Moskalev, Distribution of Antimony-124 and Tellurium-1 27, in Raspredelenie, 
Biologicheskoe Deistvie, Uskorenie Vyvedeniya Radioaktivnykh Izotopov, pp. 62—70, 
Meditsina, Moscow, 1964. (In Russian) 

10. B. Busnardo and F. Casson, Aspects of Fecal Iodine Excretion in Man, Acta Isotop., 5: 
5-13 (1965). 

11. P. L. Wright and M. C. Bell, Comparative Metabolism of Selenium and Tellurium in 
Sheep and Swine, Amer. J. Physiol., 211: 6-10 (1966). 

12. V. R. Sastry and L. K. Owens, Fission Products: Retention and Elimination of the 
Parent — Daughter Radionuclide Pair Barium-140— Lanthanum-140 by Rats, Toxicol. 
Appl. Pharmacol, 9: 431-444 (1966). 

13. S. V. Kaye, Distribution and Retention of Orally Administered Radiotungsten in the 
Rat, Health Phys., 15: 399-417 (1968). 

14. H. Kleinsorge, Absorption of Therapeutic Gold Salts and Gold Sols, Arzneim.-Forsch., 
17: 100-102 (1967). 



RADIONUCLIDE BODY BURDENS AND HAZARDS 
FROM INGESTION OF FOODSTUFFS 
CONTAMINATED BY FALLOUT 



YOOK C. NG* and HOWARD A. TEWESt 

* Bio-Medical Division and tK Division, 

Lawrence Radiation Laboratory, University of California, 

Livermore, California 



ABSTRACT 

A method developed for predicting the internal dose that could result when radionuclides 
are released to the atmosphere and deposited on agricultural land has been used to extend 
earlier studies of the problems associated with food contamination following a nuclear 
attack. The study considers activation products as well as fission products and attempts to 
take into account recent data on retention and rate of loss by weathering of both small and 
large particles on plants, on uptake of nuclides into dietary constituents, and on biological 
availability of nuclides in nuclear debris. In this study potential levels of food contamination 
and internal dose commitment are estimated both for the immediate postattack period and 
for the year closely following the attack when the initial deposition rates of stratospheric 
debris would be highest. The results are discussed in the light of the modifying factors that 
would influence them. 



A method for predicting the internal dose that could result when radionuclides 
are released to the atmosphere and deposited on agricultural land was 
developed to assess the potential burden and dosage to man which could result 
from the release of nuclides to the biosphere from any source. By means of this 
analysis, we can identify the nuclides that could contribute most to the internal 
dose and determine the contribution of each nuclide to the total dose. 

This paper considers the application of this method to examine possible 
postattack levels of contamination of terrestrial foods and the dosages that could 
result from their consumption and extends earlier studies of the problems 
associated with food contamination immediately following a nuclear attack. 2 
The work considers activation products as well as fission products and takes into 
account more-recent data on retention of small and large particles on plants and 
their subsequent rate of loss by weathering, on uptake of nuclides into dietary 



131 



132 NGANDTEWES 

constituents, and on biological availability of nuclides in nuclear debris. It also 
attempts to assess the levels of food contamination that could result from the 
initial deposition rates of the nuclear debris injected into the stratosphere. 

We make certain simplifying assumptions in order to apply our models to 
estimate the potential levels of contamination of foods and the internal dose 
commitment to man. We then examine the results and note how various 
modifying factors would influence them. 

METHOD FOR ESTIMATION OF DOSAGE 

Our predictive model combines source, transport, and interaction terms to 
estimate possible levels of contamination of foodstuffs and possible internal 
dosages that could result from their consumption. "Source" refers to the 
radionuclides produced and their quantities. The source term consists of the 
activity of each radionuclide produced in the detonation. "Transport" refers to 
the transport of nuclides from the site of detonation and their subsequent 
distribution to the biosphere. The combination of transport and source terms 
yields either the deposition or the rate of deposition from the atmosphere. 
"Interaction" refers to the interaction of the nuclides with the biosphere, i.e., 
their entry into food chains and subsequently into the tissues of man. The 
interaction terms directly relate deposition or deposition rates and air 
concentrations to levels of contamination in foods and to internal dosages. The 
general approach is described in detail elsewhere, ' and the input parameters 
required for the analysis are available in a continuously updated handbook.* 

The present analysis is confined to contamination of terrestrial foods as a 
result of foliar contamination bv fallout. Early deposition of local and 
tropospheric fallout would usually result in a far greater level of contamination 
of vegetation than that from subsequent root uptake of the fallout deposited on 
soil. Similarly, the early rates of deposition of stratospheric debris can be 
expected to cause higher levels of plant contamination than would subsequent 
root uptake from the cumulative deposition in soil. 

This analysis focuses on the forage— cow— milk and plant— herbivore— meat 
pathways. Both milk and meat are important constituents of the human diet, 
and much is known regarding their input parameters. Since relatively large 
contaminated areas can be grazed daily bv cows and other herbivores, the milk 
and meat pathways are important for many nuclides. For milk the period 
between the deposition of fallout and the ingestion of the contaminated food 
can be especially short. 



*No attempt is made in this paper to list the input parameters used in the calculations. 
Input parameters and a comprehensive bibliography of the sources from which they were 
obtained appear in a continuouslv updated handbook. Many of the parameters used are 
updated values that will appear in the forthcoming revision of the handbook. This issue will 
be available on request. 



RADIONUCLIDE BODY BURDENS 133 

This analysis considers both the immediate postattack impact on food 
contamination, which is attributable to local and tropospheric fallout, and the 
longer-term impact, which is attributable to the continuous deposition of 
nuclides from the stratosphere. 

Case studies of hypothetical nuclear attacks on the United States provide a 
useful frame of reference for the analysis of problems relating to civil defense. 
For example, two cases of hypothetical attacks, the CIVLOG and the UNCLEX, 
were used as starting points in planning for postattack recovery. 7 Other cases of 
hypothetical attacks were used by Brown and his associates at the Stanford 
Research Institute in the assessment of "national entity vulnerability." The 
general magnitude and structure of these attacks in large measure compare with 
those of CIVLOG and UNCLEX. 

For the immediate purpose of predicting the dosage that could result from 
the ingestion of contaminated foods, we do not need to make fine distinctions. 
Thus we have simply adopted some of the features of these case studies. We 
arbitrarily assumed an attack of about 1000 surface-detonated weapons with a 
total yield of 4000 Mt. These weapons are assumed to be half-fission half-fusion 
devices with individual yields between 1 and 10 Mt. It will be readily apparent 
how the results would scale with other combinations of total and individual 
yields. 

RADIONUCLIDE SOURCE TERMS 

The radionuclides produced by the detonation of thermonuclear weapons 
include fission products, activities induced in device and environmental 
materials, and tritium. In this section source terms arc derived for the 1-Mt-yield 
explosive, which is taken as the unit to be scaled linearly to higher vields. 

Fission Products 

Fission products derived from weapons test have been studied extensively 
over the past 20 years. We used the fission yields listed by Weaver et al. 

Neutron-Activation Products of Device and Environmental Materials 

From the standpoint of potential external dose from the fallout gamma 
field, the fission products resulting from the hypothetical half-fission half-fusion 
1-Mt explosive represent the most important contribution, although nuclides 
resulting from neutron interactions with unburned fissionable material can 
represent up to 40% of the total activity of the weapon debris. 9 However, 
because of special concentrating mechanisms, "minor" neutron-activation 
products could still contribute appreciablv to the internal dose following their 
entry into certain food chains. Therefore the total production is estimated for a 
number of these activation products that were not considered heretofore in the 
estimation of fallout fields from weapon detonations. 



134 NGANDTEWES 

Activation of Unreacted Fissionable Materials 

Predominant isotopes in the category of unreacted fissionable materials are 
237 U, 239 U, 239 \ T p, and 240 Np (Ref. 9). However, neither the 239 U nor the 
240 Np source terms are estimated since their relatively short half-lives (23.5 min 
and 60 min, respectively) preclude their contributing to internal doses delivered 
via food chains. 

Kimura, 10 as quoted by Miller, 1 ! indicates that for the Bravo detonation, 
there were 0.3 neutron captures per fission in U; thus for 500 kt of fission a 
total of 2.2 X 10 25 atoms of the mass-239 chain ( 2 3 9 U -> 2 39 Np -> 2 3 9 Pu) 
would be produced. This estimate can be compared with that of Langham and 
Anderson 12 that 3600 Ci of 239 Pu are produced per megaton of fission (the 
equivalent of about one neutron capture per fission in " U). This more 
conservative estimate is used in the present assessment. Kimura determined 
that approximately 0.15 atom of 237 U per fission was produced by the Bravo 
event of 1952. Using this source term, we find that 500 kt of fission results in 



Activation of Device Materials (Including Canister) 

A considerable bodv of work has been reported on atmospheric concentra- 
tions and burdens of radioactive species produced during the nuclear tests of 
1961 and 1962. Summaries bv Feely etal. 13 and by Thomas etal. 14 indicate 
that the stratospheric residence half-time of all weapon-produced radionuclides 
is approximately 10 months; hence total atmospheric burdens of the predomi- 
nant radioactive species measured in 196 3 or later must characterize uniquely 
the 1961 — 1962 injections. 

As confirmation of this hypothesis. Feely et al. 1 3 determined that the total 
atmospheric burden of Sr (corrected to July 1, 1962) was 10 MCi; since the 
total fission yield of the 1961 — 1962 atmospheric detonations has been 
estimated as 101 Mt 15 and the 90 Sr production from a "typicai" device has 
been reported as 0.1 MCi per megaton of fission,* " we can see that the 
measured burden represents essentiallv the total calculated inventory of Sr. At 
the same time, Feely et al. found the total atmospheric burden of ' Mn to be 
about 57 MCi (corrected to July 1. 1962); this represents a production source 
term of about 0.0056 atom per fission. 

In an independent study, Thomas et al. determined that the activity ratio 
of Mn to l 37 Cs. as measured on filters mounted on high-volume near-surface 
air samplers, was about 3.9. If we assume that 0.14 MCi of 137 Cs is produced 
per megaton of fission, we find that the production source term for " Mn is 
0.0036 atom per fission. When the two determinations are averaged, the 
production of 54 Mn appears to be of the order of 0.0046 atom per fission. Since 



*As quoted by Eisenbud. 



RADIONUCLIDE BODY BURDENS 



135 



the total yield of the 1961 — 1962 detonations 1 5 was 337 Mt, an average source 
term of 1 .4 X 10 s Ci of 5 Mn per megaton of total yield can be inferred. 

Table 1 summarizes activity ratios for a number of radionuclides measured in 
air and gives the references from which the ratios were abstracted. This table also 
includes some heretofore unpublished isotope ratios measured in debris from the 
Schooner event. 



Table 1 



^4 



,TTY RATIOS (RELATIVE TO ""'Mn) FOR A NUMBER 
OF NEUTRON ACTIVATION PRODUCTS 



Nuclide 



Activity ratio* 






(Relative to - Mn) 


Source 


Ref 


1.4 x 10" 3 


1961 1962 test series 


14 


6700 


Schooner 


63 


2.0 


1961-1962 test series 


64 


0.091 


Schooner 


63 


0.65 


Schooner 


63 


3.1 


Schooner 


63 


2.2 x 10 3 


1961-1962 test series 


14 


2.4 x 10^ 


1961-1962 test series 


14 


2.2 x 10 3 


1961-1962 test series 


14 


9.3 x lO^ 4 


1961-1962 test series 


14 



Na 
Mn 



Fe 
Fe 



57 



58 



Co 



Co 



Zn 

1 10m 



Ag 



Cs 



* Activity ratios obtained from debris resulting from the 1961 — 1962 
test series were calculated for July 1, 1962; activity ratios from the 
Schooner experiment were corrected to the time of detonation. 



Activation of Environmental Materials 

One of the potentially significant radionuclides created bv nuclear detona- 
tions conducted in the atmosphere is 14 C. Machta 18 estimates that the total 
production over all atmospheric tests to date is 9.17 X 10 28 atoms; since the 
cumulative yield of such tests 15 is about 511 Mt, the average production is 
about 20,000 Ci/Mt. 

Since most of the nuclear tests of the 1961 — 1962 series were airbursts, 
smaller quantities of soil activation products were produced and injected into 
the atmosphere than would be expected from surface bursts of the same total 
megatonnage. Certain radionuclides of environmental origin can be expected to 
be potentially important contributors to the internal radiation dose following 
entry into food chains and consumption bv man. For example, P, Na, 
86 Rb, 45 Ca, 84 Rb, 134 Cs, 47 Ca, and 22 Na are neutron-activation products of 
soil and rock that are potentially important via milk. 1 Except for 2 2 Na and 

Cs, measurements of neutron-activation products of soil and rock produced 
by nuclear device testing have not been reported in the open literature. The 



136 NGANDTEWES 

production of these nuclides was therefore estimated using a calculational 
approach previously reported in the literature. 

The neutron-activation calculations assume that 14-MeV neutrons are 
incident on granite. By assuming 14-MeV neutrons, we maximize the production 
of 84 Rb, 47 Ca, and 22 Na. The neutron yield per megaton of fusion is assumed 
to be 1 .45 X 10 2 7 neutrons, the oft-cited figure assumed by Leipunsky. 2 ' If we 
accept the estimate of * C production reported in this section and assume that 
essentially all the neutrons released to the environment are captured by 
atmospheric nitrogen with the resultant formation of 14 C, some 2X 10 26 
neutrons are released to the environment per megaton of fusion. This assumption 
is not unreasonable since most of the nuclear tests of the 1961 — 1962 series were 
airbursts and since the bulk of the neutron-absorption cross section of the 
atmosphere is attributable to nitrogen. Furthermore, the calculations of Lessler 
and Guy 19 indicate that for airbursts at a height of 1000 m only about 1% of 
the neutrons released to the environment are captured by soil at ground level. 

The release of 2 X 10 neutrons per megaton combined with the total 
production of 1.45 X 10 27 neutrons per megaton of fusion suggests that some 
13 to 14% of the neutrons produced are released to the environment. This 
compares with the 20% escape fraction previously assumed bv Libbv. Our 
estimates therefore assume that 400 moles of neutrons per megaton of fusion are 
released to the environment; this is equivalent to an escape fraction of about 
one-sixth. One-half of the neutrons escaping the device (i.e., 200 moles per 
megaton of fusion) are assumed to be captured in rock or soil following a surface 
detonation. Estimates of the production of 22 Na and 134 Cs based on the 
activity ratios of Table 1 suggest that, in the 1961 — 1962 test series, 3 to 4 moles 
of neutrons were released to soil per megaton. This observation is not 
inconsistent with our assumption if we remember that the 1961 — 1962 
detonations were largely airbursts. Furthermore, special neutron-shielding 
materials would have to be employed to reduce the neutrons released to the 
environment to levels as low as 3 or 4 moles per megaton of fusion. 



Tritium 

Dose estimates from tritium are considered elsewhere in this volume, but 
its source term is included here for the sake of completeness. Leipunsky 
indicated that the amount of residual tritium per megaton of thermonuclear 
yield was about 0.7 kg. Miskel 2 5 gave a range of from 0.7 to 5 kg/Mt, and, more 
recently, Tewes 2 6 reported that the residual tritium was on the order of 2 kg per 
megaton of thermonuclear yield. We will use the Tewes estimate. 

Summary of Radionuclide Source Terms 

The data in the preceding section are summarized in Tables 2 and 3. Table 2 
lists the source terms for fission products, and Table 3 lists the source terms for 



RADIONUCLIDE BODY BURDENS 



137 



Table 2 

FISSION-PRODUCT SOURCE TERMS 
FOR 1-MT FISSION EXPLOSIVE 



Nuclide 


Curies produced* 


Nuclide 


Curies produced* 


8 V 


1.5 x 10 7 


1 3 1 m~ 
Te 


2.0 x 10 8 


90 Sr 


8.8 x 10 4 


132 Te 


4.4 x 10 8 


"Mo 


6.2 x 10 8 


131, 


1.5 x 10 8 


103 Ru 


3.5 x 10 7 


133 


2.1 x 10 9 


106 D 
Ru 


2.1 x 10 6 


1 3 6 r , 
Cs 


2.0 x 10 7 


,25 Sn 


2.6 x 1() 7 


1 37 „ 
Cs 


1.5 x 10 5 


125 Sb 


3.3 x 10 5 


140 Ba 


1.1 x 10 8 


129m Te 


6.0 x 10 5 


144 Ce 


S.6 x 10 6 



* Values are corrected to detonation time. 

tritium and activation products. Included in Table 3 are not only the specific 
production terms in atoms and curies per megaton but also the "equivalent 
fission yields" of the various species. From the standpoint of contribution to the 
gamma fallout field, neutron-activation products represent a relatively small 
fraction when compared with fission products. 

Figure 1 shows the number of curies of radioactivity resulting from the 
detonation of the hypothetical 1-Mt explosive and the decay of this radioactivity 
with time. The radionuclides produced by neutron activation of the unfissioned 
uranium represent a significant fraction of the total radioactivity during the first 
few weeks after detonation. 

We should emphasize at this point that the radioactivity source term 
developed here does not necessarilv represent that which would be produced by 
any existing nuclear weapon; however, the various radionuclides considered here 
would certainly be produced in some quantity by the surface detonation of any 
weapon. Details of device construction and variations in soil composition 
obviously could drastically affect the amounts that would be formed of almost 
every species. This work, however, is expected to give at least some guidance in 
the estimation of possible internal radiation exposures from nuclides other than 
fission products and possibly to serve to identify isotopes that could be 
especially troublesome. 

PREDICTION OF THE INTERNAL DOSAGE FROM EARLY DEPOSITION 



We define a standard fallout field as one that would deliver an exposure rate 
of 100 R/hr at 1 hr postdetonation. The total dose resulting from exposure to 
such a field starting at H + 8 hr would be about 250 R. (For a more detailed 
discussion of this subject, see Ref. 9, Chap. IX.) The total dose resulting from 
exposure beginning at H + 4 hr would be about 300 R. The dosages would 



138 NGANDTEWES 



Table 3 



TRITIUM AND ACTIVATION-PRODUCT SOURCE TERM 
FOR 1-MT NUCLEAR EXPLOSIVE* 















Equivalent fi 


ssion yield, t kt 








Total 


produced 
















Source:!: 








Dose rate 
(H + 1 hr) 


Dose (H + 1 


Nuclide 


Atoms 


Curies 


hr to °°) 


3 H 


1 


2 x 


io 26 


1.0 


x IO 7 






14 c 


2 


1.8 


xlO 26 


2 x 


io 4 






22 Na 


2 


2 x 


io 22 


4.5 


x IO 3 


3 x IO" 5 


0.25 


24 Na 


2 


3 x 


io 24 


1 X 


IO 9 


9 


60 


32 p 


2 


3 x 


io 22 


4 x 


IO 5 






42 K 


2 


3 x 


io 23 


1.2 


x IO 8 


8 x IO" 2 


0.4 


Ca 


2 


3 x 


io 22 


4 x 


io 4 . 






Mn 


3 


2 x 


io 23 


1.4 


x IO 5 


3 x IO" 4 


1.0 


56,, 
Mn 


3 


4 x 


io 23 


9 x 


IO 8 


4 


4 


5 5^ 






24 




5 






- 5 Fe 


3 


1.2 


x 10 


3 x 


10 : 






Fe 


3 


3 x 


io 21 


1.3 


x IO 4 


5 x IO" 5 


2 x 10^ 


57„ 
Co 


3 


1.1 


xlO 23 


9 x 


io 4 


3 x 10~ 5 


8 x IO" 2 


58„ 
Co 


3 


1.3 


1 1 
x 10 


4 x 


io 5 


1.1 x IO" 3 


0.7 


60- 
Co 


3 


3 x 


io 21 


3 x 


io 2 


2x IO" 6 


4 x IO" 2 


65 Zn 


3 


3 x 


io 21 


3 x 


io 3 


4x IO" 6 


1.0 x IO" 2 


82 Br 


2 


7 x 


io 20 


1.1 


x IO 5 


7 x 10~ 4 


1.1 x IO" 2 


84 Rb 


2 


7 x 


io 21 


4.5 


x IO 4 


1.1 x IO" 4 


4 x IO -2 


86 Rb 


2 


2 x 


10 


2 x 


io 5 


6 x IO" 5 


1.1 x 10~ 3 


110m Ag 


3 


3 x 


1()20 ,, 


3 x 


io 2 


2 x IO" 6 


5 x 10~ 3 


134 Cs 


2 


1.8 


xlO 22 


5 x 


io 3 


2 x IO" 5 


0.16 


237 u 


4 


1.1 


xlO 25 


4 x 


io 8 


0.14 


9 


239 Np 


4 


7 x 


io 25 


6 x 


io 9 


3 


70 



*Values are calculated exclusive of fission products and assuming 500 kt of fission and 
500 kt of fusion yield. 

tThe equivalent fission yield ~ of a radionuclide, expressed as a dose rate at H + 1 hr, is 
defined as "that amount of fission required to produce fission products which, at 
H + 1 hour, will emit gamma-ray energy at the same rate as does the amount of the 
particular radionuclide under consideration." Similarly, the equivalent fission yield of a 
radionuclide, expressed as total dose delivered after H + 1 hr, is defined as "that amount of 
fission required to produce fission products which will emit (after H + 1 hour) the same 
total amount of gamma-ray energy as will the amount of the particular radionuclide under 
consideration." 

iThe numbers indicate the following sources: 1, residue from thermonuclear reactions; 
2, from neutron activation of environmental material: 3, from neutron activation of 
explosive components; and, 4, from neutron activation of unfissioned uranium. 



RADIONUCLIDE BODY BURDENS 



139 




10 100 

POSTDETONATION TIME, hr 



1000 



Fig. 1 Radioactivity from 1-Mt explosive with a fission-to-fusion ratio of 1.0. 
The activity values are derived from Tahle 3. 



actually be about 0.7 as great, because of terrain shielding, and would be 
further reduced if protection were available and were utilized. Thus a unit-time 
dose rate not exceeding 100 R/hr would be compatible with effective survival of 
a substantial segment of the population. 7 Roughly 50% or more of the land 
area of the nation would be outside the 100 R/hr contour from the hypothetical 
attack. 3 ' 7 



Fractional Deposition of Early Fallout 

If we accept a theoretical unit-time dose rate of 3700 R/hr in association 
with the uniform deposition of 1 kt of fission products per square mile of 
surface, a unit-time dose rate of 100 R/hr from unfractionated fission products 
is equivalent to a deposition of 1.05 X 10 8 kt of fission products per square 
meter of surface. (See Ref. 9, Sec. 9.183-9.184.) We have assumed that the 



140 NGANDTEWES 

contributions of neutron-activation products to the gamma field are small and, 
conservatively, that a unit-time dose rate of 100 R/hr is equivalent to a 
deposition of fission products totaling 10 8 kt/m 2 . By these assumptions, an 
equivalent yield of neutron-activation products would be produced by the 
10 8 kt of fusion and would also be deposited per square meter. For a single 
1-Mt detonation, a deposition of 10~ 8 kt/m 2 corresponds to a fractional 
deposition of 10 per square meter and, for a 10-Mt detonation, to a fractional 
deposition of 10 per square meter. Fallout levels observed subsequent to 
nuclear-device testing at the Nevada Test Site indicate that fractional depositions 
in the range from 10 l l to 10 12 per square meter could be expected within 
20 hr after detonation. 28 Both neutron-activation products and fission products 
are assumed to be deposited as unfractionated activities. The implications of 
assuming unfractioned deposition are considered later. 

Initial Retention on Vegetation and Rate of Loss by Weathering 

Physical Character of Deposition 

The cloud from a single 1-Mt surface burst in the latitude band 30 to 90° N 
can be expected to stabilize between altitudes of 26,000 and 5 3,OOOft; the 
cloud from a single 10-Mt burst can be expected to stabilize 29 between 50,000 
and 100,000 ft. Calculations based on Stoke's law can be made to estimate the 
minimum size of particles that can be deposited from these elevations under the 
influence of gravity alone. (See Ref. 9, Sec. 9.186—9.187.) These estimates 
suggest that, if the 100 R/hr contour represented fallout deposited 4 to 12 hr 
after detonation, particles of diameter >200 ju would deposit inside the contour 
and particles of diameter <50 [i would deposit outside. A dominant particle- 
diameter range of 50 to 200/^ could be expected in the fallout deposited along 
the 100 R/hr contour from a single surface burst. Dry deposition of nonfalling 
particles would not be significant at these early times. 

Taking into account the total of all surface bursts contributing to the 
100 R/hr fallout field, we anticipate (1) earlier times of arrival than previously 
assumed, which means deposition of particles larger than 200 fl, and (2) 
deposition of particles less than 50 jd originating from the more distant 
detonations. Small particles could also be deposited by rain. Predictions for the 
concentrations of nuclides in foods subsequent to the deposition of fallout 
should take into account the particle-size distribution that would be encoun- 
tered. Accordingly two sets of predictions have been made. One set is based on 
data obtained from large particles, i.e., particles 50 to 200^ and greater in 
diameter; the other is based on data obtained from small particles (<30 jj.) and 
worldwide fallout. We anticipate that, in general, the estimates of higher dose 
rates would more properly be based on the estimates of food contamination 
from large particles, whereas the estimates of lower dose rates would be based on 
those from small particles. 



RADIONUCLIDE BODY BURDENS 141 

Behavior of Small Particles 

The initial retention of small particles on vegetation is based on Chamber- 
lain's analysis 3 l of data from short-term experimental releases of vapors and 
aerosols. The fraction of the deposited activity initially retained on vegetation, 
p, is approximated by the relation 

1 — p = exp — fiw ( 1 ) 

where /i is the absorption coefficient in square meters per kilogram and w is 
the herbage density in kilograms per square meter of dry matter. The initial 
retention of small particles (^ 30 jd in diameter) on grass was characterized bv jjl 
values of 2.3 to 3.3 m 2 /kg. On the basis of Chamberlain's analysis, the initial 
retention factor for herbage densities between 0.2 and 0.4 kg/m would vary 
between 30 and 70%. In our treatment the initial retention factor for small 
particles on forage is assumed to be two-thirds (67%). 

In Thompson's review of the half-residence time and effective half-life of 
fallout on pasture plants, the half-residence time was noted to be independent of 
isotope and to vary in most cases between 9 and 14 days/ Recently 
Chamberlain 3 l examined the data obtained from field experiments on the loss 
of small-particle activity from foliage. The field-loss coefficient was found to be 
of the order of 0.05 per day during the growing season, but lower values were 
observed in winter Our estimates assume that the half-residence time of small 
particles on forage is 14 days; this is equivalent to a rate of loss by weathering of 
0.05 per day. 

Behavior of Large Particles 

Table 4 is a summary of data obtained from field experiments by 
Witherspoon and Taylor ~ and Johnson and Lovaas' ' on the initial retention 
of large-particle fallout simulant on forage plants. The table also includes 
retention data of volcanic particles as reported by Miller. 36 The initial retention 
is expressed where possible both as the percentage of fallout initially intercepted 
and retained by foliage and as the plant contamination factor, a. The plant 
contamination factor was defined by Miller as 

_ activity per unit mass dry matter on foliage 
activity per unit area of ground 

A main feature of the design of the experiments of Table 4 is the early sampling, 
which permitted the measurement of plant retention before significant field 
losses could occur. 

We excluded from Table 4 the initial retentions obtained under "damp" 
conditions (relative humidity >90%). Plant contamination factors of volcanic 
particles as reported by Miller were enhanced by about a factor of 2 under damp 



142 



NG ANDTEWES 



Table 4 
INITIAL RETENTION OF LARGE PARTICLES ON FORAGE PLANTS 









Initial retention 
















Aver 


age 






Particle 




Average 


or range. 


Wind, 


Rain, 




Species 


diameter, /i 




range), % 


m 2 


kg 


mph 


in. 


Ref. 


Lespedeza 


44 to 88 


7.5 




3.71 




to 7 


2.5 to 3 


33 




88 to 175 


1.9 




0.93 




to 7 


2.5 to 3 


33 


Alfalfa 


88 to 175 


6.5 

17 




0.45 
0.8 




6 

to 10 




35 
35 






23 (16 to 35) 


1.1 




None 


Trace 


34, 35 






7.2 


(5 to 12.2) 


0.28 




to 20 




34, 35 




175 to 350 


15 

3 

6 




0.65 
0.17 
0.25 




4 
6 
2 to 10 


Dew 


35 
35 
35 






5 (2 


.1 to 13.1) 


0.24 




None 




34. 35 


Bromegrass 


88 to 175 


4.5 




0.3 




6 




35 






7.4 (3.1 to 10.9) 


0.74 




None 


Light rain 


34, 35 




175 to 350 


0.4 




0.04 




7 




35 






5.5 


(4.6 to 6.3) 


0.55 






Trace 


34. 35 


Sundan grass 


88 to 175 


8.5 




0.4 




2 to 4 




35 




175 to 350 


7.5 




0.25 




2 to 4 




35 


"Grass" 


* 






6.7 




to 2 




36 


Barley grasst 


* 






2.4 to 


12.6 


1 to 8 




36 


Oat grasst 


* 






2.4 to 


7.3 


1 to 8 




36 


Rye grasst 


* 






2.2 to 


10.4 


1 to 9 




36 


Wheat grasst 


* 






2.1 to 


10.4 


1 to 9 




36 



*Estimated range of particle size is 10 to 250 m. and mass median diameter is ~50 to 

80 m. 

tWith reference to cereal grains, "grass" means the aerial parts prior to the development 
of grain heads. 



conditions of exposure. In this connection Johnson and Lovaas noted that the 
retention on bromegrass of particles 88 to 350 /i in diameter approached or 
reached 100% in the presence of heavy dew. We also excluded measurements 
obtained when exposure was accompanied by strong winds (>20 mph). Typical 
amounts of rain were encountered during some of the experiments represented 
in Table 4. 



33 



,34 ,35 



The data of Witherspoon and Taylor and Johnson and Lovaas 
suggest that 0.5 to 0.6 m 2 /kg might be a typical value for the plant 
contamination factor for 88- to 35 0-,a particles on forage plants. Under these 



RADIONUCLIDE BODY BURDENS 143 

conditions a cow consuming 10 to 12 kg of dry matter per day would effectively 
graze about 5 to 7 m of contaminated land per day. This is about one-fifth of 
the 30 m 2 /day assumed to be utilized by the cow when small particles are 
deposited ["utilized area factor" (UAF), 45 m 2 /day; plant retention factor, 
0.67]. Miller's data 36 suggest that the plant contamination factor for local 
fallout on forage plants would be an order of magnitude greater, i.e., about 5 to 
6 m 2 /kg. The land area effectively utilized daily by a cow consuming 10 to 
12 kg/day of dry matter would then be about 60 m 2 /day, which is comparable 
within a factor of 2 to the area assumed to be utilized by the cow when small 
particles are deposited. The volcanic ash studied by Miller apparently was of a 
somewhat smaller range of particle sizes, having a maximum diameter of about 
240 ii and a mass median diameter we estimate to be about 50 to 80 jjl, as far as 
can be determined. Interestingly, a plant contamination factor of 3.7 m 2 /kg was 
obtained by Witherspoon and Taylor for 44- to 88-fJi particles on lespedeza. 

The half-residence time of large particles on forage plants was also studied in 
these experiments. In the experiments of Witherspoon and Taylor, 33 the 
retention curve of simulated fallout particles on crop plants was characterized by 
a number of weathering half-lives. We estimated the integrated retention on 
lespedeza from these data and found it to be about 5.4 days for 44- to 88-/i 
particles and 6.7 days for 88- to 175-jU particles. If we assume a simple 
exponential retention function, these integrated retentions correspond to a 
half-residence time of 3.7 to 4.7 days. In the experiments of Johnson and 
Lovaas, 35 less rainfall occurred and somewhat longer half-times were noted. 
Half-times on alfalfa, bromegrass, and sudan grass were about a week or longer. 
Miller's data on volcanic particles suggest a much more rapid rate of loss by 
weathering, with half-times being measured in hours. For example, on the basis 
of the median wind-weathering factor obtained for broadleaf grasses, the 
field-loss coefficient would be 0.2 per hour when the average wind speed is 
2 mph; this is equivalent to a half-residence time of 3.5 hr (about 0.15 day), 
which represents about a hundredfold reduction of the 14-day half-residence 
time assumed for small particles on forage. On the other hand, a small fraction 
of the particles deposited on vegetation, of the order of 2 to 10%, was found to 
be "nonremovable" and was quantitatively retained. 

The effect of large-particle deposition on the estimates of food contamina- 
tion and dosage is evaluated later by assuming a plant contamination factor of 
0.5 m 2 /kg, in accord with the observations of Witherspoon and Taylor 33 and 
Johnson and Lovaas. 34 ' 35 A plant contamination factor of this magnitude is 
equivalent to a retention of 12 to 13%, which is about one-fifth that assumed for 
small-particle deposition. The estimates for large-particle deposition will be made 
assuming a half-residence time on forage of 4 days. This is consistent with our 
integrated retention calculated from the observations of Witherspoon and Taylor 
and does not depart significantly from the somewhat longer half-times observed 
by Johnson and Lovaas. 



144 NGANDTEWES 

Forage-Cow-Milk Pathway (Small Particles) 

In the forage— cow— milk model, 1 the fallout deposited on pasture is 
continuously ingested by the grazing cow. The UAF is assumed to be 
45 m 2 /day; i.e.. the cow is assumed to utilize 45 m 2 of pasture daily. This value 
is based on Koranda's review of agricultural factors affecting the intake of dairv 
cows, in which a median UAF value of 45 m 2 /day was found for dairy cows in 
the United States. 37 The initial daily rate of ingestion by the cow of a given 
nuclide (I ) m microcuries per day is then given bv 

I = R X UAF X F (2) 

where R is the initial retention factor and F is the initial deposition in 
microcuries per square meter. In presenting the estimates of food contamination 
and dosage, we report the results for small particles first since they are higher. 
Please recall that R is assumed to be 0.67 for small particles. 

Concentration of Nuclides in Milk 

Tables 5 and 6 list the estimated peak concentrations in milk from the 
deposition of small particles; Table 5 shows the results for fission products and 
Table 6 the results for activation products. In these tables f^ is the transfer 
coefficient to milk, the fraction of the element ingested dailv bv the cow which 
is secreted per liter of milk. These transfer coefficients include corrections for 
the observed biological availability, where it is known, of the nuclide in fallout. 6 
Some of the correction factors were obtained bv Potter in experiments of 

the kind reported in this volume. 

The peak concentrations in milk. Cm, are given both as the fraction of the 
initial daily intake, I , per liter and in microcuries per liter. The concentrations 
were calculated on the basis of the rate of disappearance of nuclides in milk 
following a single administration to the lactating cow. If the turnover rate of a 
nuclide in milk was not available from the literature, an instantaneous steady 
state was assumed with respect to the secretion of activity in milk following 
deposition on forage. In these cases. Cm expressed as a fraction of I is 
numerically the same as f\^. Note that input parameters are well known for the 
nuclides that contribute most to the dosage. 

Estimated Dosage via Milk 

Tables 7 and 8 present the dosage estimates via milk from the deposition of 
small particles. Table 7 presents the estimates for fission products and Table 8 
those for activation products. The first column of each table lists the total 
activity ingested assuming milk consumption at the rate of 1 liter/day. The 
second and third columns of each table list the dose commitment to the whole 
body and bone of an adult. As previouslv recognized, the nuclides that 



RADIONUCLIDE BODY BURDENS 145 



Table 5 

ESTIMATED PEAK CONCENTRATION IN MILK FROM 

DEPOSITION OF SMALL PARTICLES (FISSION 

PRODUCTS ONLY)* 







C M t 






Fraction of 




Radionuclide 


f]Vi /liter /day t 


I per liter 


/iCi/Iiter 


89 Sr 


9.0 (-4) 


6.7 (-4) 


3.1 (0) 


90 Sr 


9.0 (-4) 


7.2 (-4) 


1.9 (-2) 


99, „ 
Mo 


7.5 (-4) 


3.5 (-4) 


6.5 (1) 


1 03 
Ru 


1.0 (-6) 


1.0 (6) 


1.0 (-2) 


1 06 D 
Ru 


1.0(-6) 


1.0 (-6) 


6.3 (-4) 


Sn 


1.0 (-3) 


1.0(-3) 


8.0 (0) 


1 25 c , 
Sb 


5.0 (-6) 


5.0 (-6) 


4.9 (-4) 


1 29m„ 
Te 


1.25 (-4) 


8.3 (-5) 


1.5 (-2) 


1 3 im T 
le 


1.25 (-4) 


2.3 (-5) 


1.4(0) 


13 2™ 
Te 


1.25 (-4) 


4.3 (-5) 


5.6 (0) 


131 


5.0(-3) 


2.5 (-3) 


1.1 (2) 


133. 


5.0 (-3) 


1.0 (-3) 


4.6(2) 


136 Cs 


7.5 (-3) 


3.2 (-3) 


1.9 (1) 


137 Cs 


7.5 (-3) 


4.8 (-3) 


2.1 (-1) 


1 40„ 
Ba 


1.5 (-4) 


7.8 (-5) 


5.1 (0) 


1 44^, 
Ce 


2.0 (-5) 


2.0 (-5) 


2.1 (-2) 



*Deposition is assumed to be 10 kt of fission products per 
square meter. 

tThe numerical value in parentheses signifies the exponential 
power of 10; thus 9.0 (-4) signifies 9.0 x 10" 4 . 



contribute most to the dose commitment via milk are the fission products Sr, 
90 Sr, "Mo, 132 Te, l31 I, 133 I, 136 Cs, l 3 7 Cs, and » 4 ° Ba and the activation 
products of soil and rock, 22 Na, 24 Na, 32 P, 45 Ca, 47 Ca, 84 Rb, 86 Rb, and 
134 Cs. All the parameters required for the forage— cow—milk model are 
adequately known for all these nuclides. Activation products of device materials 
do not contribute appreciably to the total dose commitments. The isotopes 
whose input parameters via milk are not well known include Sn (Table 7) 

and 110m Ag, 237 U, and 239 Np (Table 8). Since conservative estimates were 
assumed, the dosages may be overconservative. These isotopes, however, do not 
make substantial contributions to the total dosage. 

The estimates of dosage to the whole body and bone via milk (Tables 7 and 
8) should be compared with the corresponding estimates for the thyroid. For the 
adult thyroid the dosage estimate corresponding to the 4.6-rad whole-body 
dosage from l 3 * I j s 2500 rads; the corresponding estimate from l 3 3 I is 500 rads 
(assuming deposition occurs at 8 hr postdetonation). 



146 NGANDTEWES 



Table 6 



ESTIMATED PEAK CONCENTRATION IN MILK FROM 

DEPOSITION OF SMALL PARTICLES (ACTIVATION 

PRODUCTS ONLY)* 







C M t 






Fraction of 




Radionuclide 


f]V|/liter/dayt 


I per liter 


^iCi /liter 


2 1 

Na 


1.5 (-2) 


4.5 (-3) 


1.4 (-2) 


24 VT 

Na 


1.5 (-2) 


1.9 (-4) 


1.1 (2) 


32 p 


2.0 (-2) 


1.3 (-2) 


3.3 (0) 


42 K 


5.0 (-3) 


2.8 (-4) 


2.0(1) 


45 Ca 


1.4 (-2) 


1.1 (-2) 


2.7 (-1) 


4 7„ 

Ca 


1.4 (-2) 


7.3 (-3) 


1.3 (-1) 


54 Mn 


1.0 (-5) 


1.0 (-5) 


4.2 (-4) 


55 Fe 


4.0 (-5) 


4.0 (-5) 


3.6 (-3) 


59 Fe 


4.0 (-5) 


4.0 (-5) 


1.6 (-4) 


5 7,-, 

Co 


4.0 (-4) 


4.0 (-4) 


1.1 (-2) 


Co 


4.0 (-4) 


4.0 (-4) 


4.9 (-2) 


Co 


4.0 (-4) 


4.0 (-4) 


3.6 (-5) 


65 7„ 

Zn 


1.0 (-2) 


1.0 (-2) 


9.0 (-3) 


82 Br 


1.1 (-2) 


1.1 (-2) 


7.4 (-1) 


84 Rb 


1.5 (-2) 


8.4 (-3) 


2.3 (-1) 


86 Rb 


1.5 (-2) 


7.5 (-3) 


1.0(0) 


l l om . 

Ag 


5.0 (-3) 


5.0 (-3) 


4.5 (4) 


134 Cs 


7.5 (-3) 


4.7 (-3) 


1.4 (-2) 


237 u 


1.5 (-4) 


1.5 (-4) 


1.8 (1) 


239 Np 


5.0 (-5) 


5.0 (-5) 


9.0(1) 



*Deposition is assumed to be 10 kt of neutron-activation 
products from fusion per square meter. 

tThe numerical value in parentheses signifies the exponential 
power of 10; thus 1.5 ( — 2) signifies 1.5 x 10 . 



Plant— Herbivore— Meat Pathway 

Since most of our cattle and sheep remain on pasture throughout the year, 
meat potentially could contribute relatively large quantities of nuclides to the 
diet following their deposition on vegetation. The plant— herbivore— meat model 
represents a preliminary attempt to evaluate the importance of meat contamina- 
tion following the release of nuclides to the biosphere. In the model the fallout 
deposited on pasture is continuously ingested by grazing livestock and deposits 
in their muscle. The concentration of nuclides in the muscle of the 500-kg 
standard herbivore having a muscle mass of 200 kg was estimated from the daily 
rate of ingestion of contaminated vegetation and the turnover rate in muscle. 



RADIONUCLIDE BODY BURDENS 



147 



Table 7 

ESTIMATED DOSAGE VIA MILK TO WHOLE BODY AND BONE 
FROM FISSION PRODUCTS DEPOSITED AS SMALL PARTICLES 



Radionuclide 



Total activity ingested,*! 
juCi 



Dose commitment,*:!: rads 



Whole body 


Bone 


0.56 


4.4 


0.70 


5.7 


0.45 


0.63 


7 (-4) 


1 (-3) 


5 (-4) 


1 (-3) 


0.028 


0.13 


4 (-6) 


1 (-5) 


9 (-4) 


1.4 (-3) 


2 (-3) 


2.3 (-3) 


0.054 


0.06 


4.6 


2.4 


0.93 


0.68 


5.9 


5.9 


0.45 


0.45 


0.13 


0.95 


1 (-5) 


4 (-5) 



99 A , 
Mo 

1 03 



Ru 
Ru 



1 i O ^ 

Sn 

1 25 ol 
Sb 

129m 

1 3 lm T 



Te 



133, 



1 37 
140 



Cs 
Cs 
Ba 
Ce 



6.5 (1) 


4.8 (-1) 


3.5 (2) 


1.6 (-1) 


1.2 (-2) 


4.8 (1) 


9.7 (-3) 


3.0(-l) 


4.8(0) 


4.1 (1) 


1.3 (3) 


1.2 (3) 


3.5 (2) 


6.7 (0) 


8.1 (1) 


4.1 (-1) 



Total dose commitment 



14 



21 



*The numerical value in parentheses signifies the exponential power of 10; 
thus 6.5 (1) signifies 6.5 x 10 . 

tValues are based on a daily intake of 1 liter of milk having radionuclide 
concentrations as listed in Table 5. 

rfDose commitment is calculated as the 30-year dose to an adult (standard 
man). 



For these estimates conservative but reasonable values were assumed for the 
fractional uptake to muscle by ingestion; these uptake values were estimated on 
the basis of experimental data from animals. The studies of Potter 39 and 
Chertok, as reported in this volume, were useful for this purpose. The 
biological half-life in muscle was then estimated from these fractional uptakes 
and from the stable-element concentrations in meat and forage plants as 
reported in the literature. Minor corrections were applied to the fractional 
uptakes and turnover rates on the basis of radionuclide burdens reported for 

Details of this procedure will be reported 



4 2 ,4 3 



90 



animal muscle and vegetation 

subsequently. The fractional uptake and turnover rates of vu Sr, 

are comparable with previously 7 assumed values/ 



1 3 1 



I, and 



Cs 



148 NGANDTEWES 



Table 8 



ESTIMATED DOSAGE VIA MILK TO WHOLE BODY AND BONE 
FROM ACTIVATION PRODUCTS DEPOSITED AS SMALL PARTICLES 





Total activity- ingested, *t 

AiCi 


Dose commitment 


,* i rads 


Radionuclide 


Whole body 


Bone 


22 Na 


3.1 (-1) 


0.015 


0.015 


24 Na 


1.3 (2) 


0.22 


0.022 


32 p 


4.6 (1) 


0.34 


1.95 


42 K 


1.3 (1) 


0.011 


0.011 


45 „ 
Ca 


5.9 (0) 


0.05 3 


0.52 


47„ 
Ca 


1.3 (0) 


0.0042 


0.041 


Mn 


8.1 (-3) 


1 (-5) 


7 (-5) 


5 5^ 
Fe 


7.1 (-2) 


2 (-5) 


3 (-5) 


5 9 „ 
Fe 


2.4 (-3) 


9 (-6) 


1 (-5) 


5 7„ 

Co 


2.1 (-1) 


1 (-4) 


9 (-5) 


58„ 

Co 


8.2 (-1) 


0.003 


0.002 


60 ,-, 
Co 


7.2 (-4) 


8 (-6) 


6 (-6) 


65 Zn 


1.7 (-1) 


0.001 


0.002 


82 Br 


1.4(0) 


0.003 


0.003 


84 Rb 


5.2 (0) 


0.18 


0.18 


86 Rb 


2.1 (1) 


0.24 


0.24 


l 1 0m , 
Ag 


8.6 (-3) 


7 (-4) 


0.001 


134 Cs 


4.5 (-1) 


0.050 


0.050 


237 U 


1.2 (2) 


0.002 


0.003 


2 39 v , 
Np 


2.6 (2) 


2 (-5) 


1 (-4) 




Total dose commitment 


1.1 


3.0 



*The numerical value in parentheses signifies the exponential power of 10; 
thus 8.1 (-1) signifies 8.1 x H)' 1 . 

tValues are based on a daily intake of 1 liter of milk having radionuclide 
concentrations as listed in Table 6. 

±Dose commitment is calculated as the 30-year dose to an adult (standard 
man). 



Concentrations of Nuclides in Meat 

Peak concentrations of nuclides in herbivore muscle were estimated assuming 
small-particle deposition. The standard herbivore, such as the cow, is assumed to 
utilize 45 m of pasture daily and actually to consume daily the small particles 
deposited on 30 m 2 (initial retention factor, two-thirds). The half-residence time 
on forage is assumed to be 14 days. 

Table 9 lists the estimated peak concentrations for fission products in 
herbivore muscle from the deposition of small particles, and Table 10 lists 
concentrations for activation products. The estimates are presented for nuclides 



RADIONUCLIDE BODY BURDENS 149 



Table 9 

ESTIMATED PEAK CONCENTRATION IN HERBIVORE MUSCLE 
FROM DEPOSITION OF SMALL PARTICLES (FISSION PRODUCTS ONLY)' 



idionuclide 


0uCi/kg)/(juCi/m 2 ) 


M Ci/kg 


89 c 
Sr 


4.9 (-3) 


4.9 (-1) 


90 e 
Sr 


5.3 (-3) 


3.2 (-3) 


1 03„ 
Ru 


1.4 (-2) 


3.2 (0) 


1 06 n 

Ru 


2.2 (-2) 


3.0(-l) 


1 25 e 
Sn 


2.5 (-2) 


4.4 (0) 


125 c , 
Sb 


6.8 (-3) 


1.5 (-2) 


1 29m„ 
Te 


2.1 (-2) 


8.5 (-2) 


13 1. 


3.2 (-2) 


3.1 (1) 


1 36 „ 
Cs 


4.5 (-1) 


6.0(1) 


13 7,, 
Cs 


1.1 (0) 


1.0(0) 


140 D 
Ba 

144,, 

Ce 


5.3 (-4) 
2.2 (-3) 


3.9 (-1) 
5.1 (-2) 



Ratio of 

Cmeat to C\i,t 
(juCi/kg)/(MCi/liter) 



0.2 
0.2 
300 
400 
0.9 
30 

6 
0.3 

3 
5 
0.08 

1 



*Deposition is assumed to be 10 kt of fission per square meter. 
tThc numerical value in parentheses signifies the exponential power of 10; 
thus 4.9 (-3) signifies 4.9 x 10 . 

|The peak concentrations in milk, Cm, are given in Table 5. 



having half-lives greater than 7 days. The coneentrations in muscle (C mcat ) in 
microcuries per kilogram are presented both for unit deposition and for the 
10 8 kt/m 2 hypothetical deposition. The last column of each table lists for each 
nuclide the ratio of peak concentration in meat to that in milk. Meat-to-milk 
ratios greater than 10 are noted for 1 ° 3 Ru, l 06 Ru, and l 2 5 Sb (Table 9) and for 
54 Mn, 5 5 Fe, and 5 9 Fe (Table 10). These nuclides were found earlier to be 
relatively unimportant via milk, but they could potentially represent a greater 
hazard via meat. 

Estimated Dosage via Meat 

Table 1 1 presents the dosage estimates for fission products via meat from the 
deposition of small particles and Table 12 the dosage estimates for activation 
products. We assumed for the estimates that the animal is slaughtered when the 
concentration in muscle is maximal and that meat consumption begins 
immediately and proceeds for a 6-month period at the rate of 300 g/day. 
Although these assumptions appear to be both overconservative and unrealistic, 
they serve to emphasize the relative unimportance of the meat pathway in 
comparison with the milk pathway. 



1 50 Table 10 

ESTIMATED PEAK CONCENTRATION IN HERBIVORE MUSCLE FROM 
DEPOSITION OF SMALL PARTICLES (ACTIVATION PRODUCTS ONLY) 1 









Ratio of 




Cmeat' r 




Cmeat to QW'4 








Radionuclide 


(MCi/kg)/(MCi/m 2 ) 


uCi/kg 


(MCi/kg)/(MCi/liter) 


22 Na 


1.0(0) 


6.1 (-2) 


4 


32 p 


2.3 (-1) 


1.3 (0) 


0.4 


45 Ca 


5.7 (-2) 


3.0 (-2) 


0.1 


54 Mn 


1.6 (-2) 


1.5 (-2) 


40 


5S Fe 


3.5 (-2) 


7.1 (-2) 


20 


59 Fe 


2.1 (-2) 


1.8 (-3) 


10 


57 Co 


2.1 (-2) 


1.3 (-2) 


1 


58 Co 


1.7 (-2) 


4.6 (-2) 


1 


60 Co 


2.3 (-2) 


4.6 (-5) 


1 


65 Zn 


2.4 (-1) 


4.7 (-3) 


0.5 


84 Rb 


5.0(-l) 


3.0(-l) 


1 


86 Rb 


4.1 (-1) 


1.2(0) 


1 


110m Ag 


7.3 (-2) 


1.5 (-4) 


0.03 


134 Cs 


1.0 (0) 


7.0 (-2) 


5 



*Deposition is assumed to be 10 kt of neutron-activation products from 
fusion per square meter. 

tThe numerical value in parentheses signifies the exponential power of 10; 
thus 1.0(0) signifies 1.0 x 10°. 

±The peak concentrations in milk C\j are given in Table 6. 



Table 11 

ESTIMATED DOSAGE VIA MEAT TO WHOLE BODY AND BONE FROM 
FISSION PRODUCTS DEPOSITED AS SMALL PARTICLES 





Total activity ingested, *t 


Dose commitment,* ± rads 








Radionuclide 


M Ci 


Whole body 


Bone 


89 Sr 


2.4 (1) 


0.087 


0.67 


90 Sr 


4.5 (-1) 


0.24 


2.0 


1 03 D 
Ru 


5.3 (1) 


0.22 


0.32 


1 06 D 
Ru 


1.4(1) 


0.59 


1.5 


125 Sn 


1.8 (1) 


8 (-3) 


0.036 


125 Sb 


7.6 (-1) 


3 (-4) 


9 (-4) 


l29m Te 


1.2 (0) 


3.6 (-3) 


5.5 (-3) 


131, 


1.1 (2) 


0.38 


0.20 


1 36,, 
Cs 


3.4(2) 


5.7 


5.7 


1 3 7„ 
Cs 


5.7 (1) 


3.9 


3.9 


140^ 

Ba 

144„ 
Ce 


2.2 (0) 


2.8 (-3) 
6 (-5) 


0.021 
2 (-4) 



Total dose commitment 11 



The numerical value in parentheses signifies the exponential power of 10; 
thus 2.4 ( 1 ) signifies 2.4 x 10 1 . 

tValues are based on a daily intake of 300 g for a 6-month period of meat 
having radionuclide concentrations as listed in Table 9. 

iDose commitment is calculated as the 30-year dose to an adult (standard 
man). 



RADIONUCLIDE BODY BURDENS 151 

Table 12 

ESTIMATED DOSAGE VIA MEAT TO WHOLE BODY AND BONE FROM 
ACTIVATION PRODUCTS DEPOSITED AS SMALL PARTICLES 





Total activity ingested, *t 


Dose commitment,* X rads 


Radionuclide 


MCi 


Whole body 


Bone 


22 Na 


3.1 (0) 


0.057 


0.057 


32 p 


7.8 (0) 


0.058 


0.33 


45 Ca 


1.2 (0) 


0.010 


0.10 


54 Mn 


6.7 (-1) 


1.2 (-3) 


5.5 (-3) 


55 Fe 


3.6(0) 


1.1 (-3) 


1.7 (-3) 


59 c 
Fe 


3.3 (-2) 


1 (-4) 


1 (-4) 


5 7 r , 
Co 


5.5 (-1) 


3 (-4) 


3 (-4) 


58,-, 
Co 


1.2(0) 


4.1 (-3) 


3 (-3) 


Co 


2.4 (-3) 


3 (-5) 


2 (-5) 


65 Zn 


2.0(-l) 


1.3 (-3) 


2.3 (-3) 


84 Rb 


4.2 (0) 


0.14 


0.14 


86 Rb 


1.0(1) 


0.11 


0.11 


1 1 0m . 

Ag 


6.3 (-3) 


5 (-4) 


8 (-4) 


134 Cs 


3.5 (0) 


0.40 


0.40 



Total dose commitment 0.78 1.2 



*The numerical value in parentheses signifies the exponential power of 10; 
thus 3.1 (0) signifies 3.1x10°. 

tValues are based on a daily intake of 300 g for a 6-month period of meat 
having radionuclide concentrations as listed in Table 10. 

^Dose commitment is calculated as the 30-year dose to an adult (standard 
man). 



The nuclides that could contribute most to the dose commitments via meat 
include some of those previously singled out in the discussion of the milk 
pathway: 89 Sr, 90 Sr, ,31 I, 136 Cs, and ' 3 7 Cs (Table 11 ) and 2 2 Na, 32 P, 45 Ca, 
84 Rb, 86 Rb, and l 34 Cs (Table 12). Of the nuclides having meat-to-milk 
concentration ratios greater than 10, only 103 Ru and 106 Ru could contribute 
substantially to the dose commitment. The input parameters required in the 
plant— herbivore— meat model for isotopes of ruthenium cannot be regarded as 
being firmly established. Activation products of device origin do not contribute 
appreciably to the dose commitments via meat. The estimates of dosage to the 
whole body and bone should be compared with the corresponding estimate for 
the thyroid from l 3 * I, a dosage of 200 rads. 

Estimated Dosage from Deposition of Large Particles 

Tables 13 and 14 present the dosage estimates for fission products and for 
activation products, respectively, via milk and meat from the deposition of large 



152 



NG ANDTEWES 



Table 13 

ESTIMATED DOSAGE TO WHOLE BODY AND BONE FROM FISSION 
PRODUCTS DEPOSITED AS LARGE PARTICLES 







Dose commitment, rads*t 






Via milkt 




Via meat § 




Radionuclide 


Whole body 


Bone 


Whole body 


Bone 


89 Sr 


0.03 8 


0.29 


0.013 


0.10 


90 Sr 


0.040 


0.3 3 


0.036 


0.29 


99,. 

Mo 


0.064 


0.089 






1 03 D 
Ru 


5 (-5) 


7 (-5) 


0.021 


0.030 


1 06„ 
Ru 


3 (-5) 


8 (-5) 


0.044 


0.11 


l25 Sn 

125 Sb 
l 29m„ 

Te 

1 3 im T 
Te 


0.007 

2 (-7) 
6 (-6) 
3.7 (-4) 


0.032 
6 (-7) 
1 (-4) 
4 (-4) 


0.001 
2 (-5) 
4 (-4) 


0.005 
6 (-5) 
6 (-4) 


132 Te 


0.007 


0.008 






131, 


0.48 


0.25 


0.05 3 


0.028 


133, 


0.16 


0.12 






1 36„ 
Cs 


0.54 


0.54 


0.71 


0.71 


1 37„ 
Cs 


0.026 


0.026 


0.32 


0.32 


140 D 

Ba 


0.010 


0.074 


3 (-4) 


0.003 


144„ 
Ce 


6 (-7) 


3 (-6) 


4 (-6) 


2 (-5) 


Total dose 


1.4 


1.8 


1.2 


1.6 


commitment 











*The numerical value in parentheses signifies the exponential power of 10: thus 5 ( — 5) 
signifies 5x10'. 

tDose commitment is calculated as the 30-year dose to an adult (standard man). 

± Values are based on a daily milk intake of 1 liter. 

§ Values are based on a daily meat intake of 300 g for a 6-month period. 



particles. Please recall that these estimates were made by assuming an initial 
retention of 13% and a half-residence time on forage of 4 days. In other respects 
the dosage estimates were made in the same manner as those from deposition of 
small particles. 



Summary of Dosage Estimates 

Table 15 summarizes the dosage estimates from deposition of small and large 
particles via milk, and Table 16 summarizes those via meat. For both routes and 
both kinds of deposition, the dose to the thyroid from iodine isotopes is the 
highest of all doses listed. The thyroid doses via milk exceed the total doses to 
whole body and bone bv two orders of magnitude and via meat by one order of 
magnitude. The dosages from fission products exceed the dosages from 



RADIONUCLIDE BODY BURDENS 



153 



Table 14 

ESTIMATED DOSAGE TO WHOLE BODY AND BONE FROM 
ACTIVATION PRODUCTS DEPOSITED AS LARGE PARTICLES 







Dose commitment, mrad*t 






Via 


milkt 


Via meat§ 




Radionuclide 


Whole body 


Bone 


Whole body 


Bone 


22 Na 
24 Na 


0.86 

41 


86 
41 


4.5 


4.5 


32 p 

42 K 


30 

2.1 


170 

2.1 


6.9 


39 


45 ~ 

Ca 


3.2 


32 


0.93 


9 1 


47 

Ca 


0.52 


5.1 






54 A „ 
Mn 


8 (-4) 


4 (-3) 


0.11 


0.5 3 


5 5 r 
Fe 


1 (-3) 


2 (-3) 


0.074 


Oil 


59,-, 
Fe 


6 (-4) 


7 (-4) 


0011 


0.012 


5 1 „ 

Co 


8 (-3) 


6 (-3) 


0.027 


0.020 


5 8^ 
Co 


0.19 


0.14 


0.35 


0.26 


Co 


5 (-4) 


4 (-4) 


0.002 


0.001 


65- 
Zn 


0.07 


0.12 


0.10 


0.18 


82 Br 


0.55 


0.55 






84 Rb 


12 


12 


16 


16 


86 Rb 


20 


20 


14 


14 


110m Ag 


0.04 


0.06 


0.04 


0.06 


134 Cs 

237 u 


3.0 

0.27 


3.0 
0.33 


34 


34 


239 VI 

Np 


3 (-3) 


2 (-3) 






Total dose 


110 


290 


77 


120 


commitment 











*The numerical value in parentheses signifies the exponential power of 10; thus 8 (—4) 
signifies 8x10 

tDose commitment is calculated as the 30-year dose to an adult (standard man). 

£ Values are based on a daily milk intake of 1 liter. 

§ Values are based on a daily meat intake of 300 g for a 6-month period. 



154 



NG ANDTEWES 



Table 15 

SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED DOSAGE 
VIA MILK FROM DEPOSITION OF SMALL AND LARGE PARTICLES* 







Small 


particles, 


rad 


s 


Large particles, 


rac 


s 


Source 


VVh 


ole body 


Bone 




Thyroid 


Whole body 


Bone 




Thyroid 


Fission 

Neutron 
activation 




14 
1.1 


21 
3 




3000t 


1.4 
0.11 


1.8 
0.29 




340t 



Total 



15 



24 



1.5 



*This table summarizes the dosage estimates of Tables 7, 8, 13. and 14. 



tThe thyroid dosage is attributed to I and I. 



Table 16 

SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED DOSAGE 
VIA MEAT FROM DEPOSITION OF SMALL AND LARGE PARTICLES* 





Small 


particles, rads 


Large 


particles, 


rat 


s 


Source 


Whole body 


Bone Thyroid 


Whole body 


Bone 




Thyroid 


Fission 

Neutron 
activation 


11 
0.78 


14 200t 
1.2 


1.2 
0.077 


1.6 
0.12 




28+ 



Total 



15 



1.3 



1.7 



*This table summarizes the dosage estimates of Tables 11, 12, 13, and 14. 



+The thyroid dosage is attributed to 



activation products by about an order of magnitude. Most of the dose 
commitment from activation products is attributable to nuclides derived from 
rock and soil. The total doses to the whole body and bone are about the same 
via milk and via meat. In view of the overconservative and unrealistic 
assumptions involved in making the dosage estimates via meat, this similarity 
serves to emphasize the much greater importance of the milk pathway following 
single depositions on vegetation. The thyroid dose from iodine isotopes via milk 
exceeds that via meat bv an order of magnitude; this further emphasizes the 
importance of the milk pathway. When we consider the dose commitment to a 
child, the importance of the milk pathway is magnified still further. For both 
pathways the dosage estimate for a child's thyroid would be higher by about a 
factor of 10 than that shown in Tables 15 and 16 for an adult. However, a child 



RADIONUCLIDE BODY BURDENS 155 

is likely to consume a liter of milk daily but would be likely to consume meat at 
a much lower rate than 300 g/day. 

The estimates of dosage from large-particle deposition are almost uniformly 
one-tenth those from small-particle deposition. The differences would be greater 
if we assumed a retention factor less than 13% and/or a half-residence time on 
forage less than 4 days. 

Uncertainties in the Estimates 

Some of the uncertainties in predicting food contamination and dosage 
relate to the assumptions adopted. In the estimates of milk contamination, we 
assumed that cows are continuously grazing on pasture. If cows were feeding on 
stored feed collected before the deposition of fallout, milk contamination could 
be expected to be lower by one to two orders of magnitude. Similarly, our 
assumption that milk consumption begins immediately with no delay for 
processing and handling leads to estimates that are overconservative for the 
particularly short-lived nuclides such as 99 Mo, ,3lm Te, 133 I, 24 Na, 42 K, and 
82 Br. The dosages would also be lower if milk consumption were delayed. 

The same considerations apply to the estimates via the meat pathway, where 
delays associated with processing and handling would be greater. As we have 
pointed out, the conservative, unrealistic assumptions adopted for the meat 
pathway serve to emphasize the much greater importance of the milk pathway 
following single depositions of radionuclides on vegetation. 

Additional uncertainties in the predictions are attributable to uncertainties 
in the transport and interaction terms. We have assumed unfractionated 
deposition of nuclides. Among the nuclides that were shown to make important 
contributions to the dosage are 89 Sr, 90 Sr, 137 Cs, and 140 Ba, which have 
rare-gas precursors. We can reasonably expect that nuclides with rare-gas 
precursors would be distributed to a greater extent on the smaller particles. 
Consequently food contamination and dosage from large particles may be 
overestimated, whereas those from small particles may be underestimated. The 
actual differences between the dosage estimates from small and large particles 
would then be greater than those shown in Tables 15 and 16. 

The actual extent of food contamination bv the other important nuclides 
singled out ("Mo, 131 I, ,36 Cs, 22 Na, 24 Na,' 32 P, 45 Ca, 84 Rb, 86 Rb, and 

Cs) depends similarly on their partitioning between small- and large-particle 
fractions. Most of these nuclides would be expected to exhibit intermediate 
behavior with respect to fractionation. The refractory nuclide 99 Mo, which 
would contribute to the dosage via milk at early times, could be expected to be 
distributed to a greater extent in the larger particles. 

The major uncertainty in the interaction term is the biological availability of 
the nuclide in fallout, which depends in turn on the partitioning of the nuclide 
between small- and large-particle fractions. The biological availabilities of 22 Na, 
89 Sr, 90 Sr, "Mo, 13, I, 133 I, » 34 Cs, 1 3 7 Cs, and l 40 Ba in small-particle debris 



156 NGANDTEWES 

(^ 50 fj.) with respect to milk secretion have been found to be comparable to 
those of tracers used in experiments within a factor of 2 or 3. The biological 
availabilities of 24 Na, 32 P, 45 Ca, 47 Ca, 84 Rb, 86 Rb, and 136 Cs have not been 
determined. The biological availabilities of some nuclides in large particles may 
be less than in small particles by virtue of differences in physical state, which 
would lead to lower estimates from large-particle deposition. 

PREDICTION OF THE INTERNAL DOSAGE FROM LONG-TERM 
DEPOSITION BASED ON CHRONIC-CONTAMINATION MODEL 

It is estimated that a land-surface burst in the 1-Mt range would inject about 
50% of its radioactivity into the stratosphere. 29 Therefore we shall assume that 
50% of the nuclides produced would enter the stratosphere and be deposited as 
long-term fallout. At the same time we can reasonably assume an equivalent 
injection into the stratosphere originating from retaliatory detonations initiated 
by friendly forces. On this basis we have simply assumed that all the activity 
produced would be injected into the stratosphere, as would be the case for 
airbursts involving weapons of the size assumed. 

Air Concentrations and Rate of Deposition of Nuclides 

The estimated rate of deposition of nuclides from the stratosphere is based 
on Peterson's empirical model for estimating worldwide deposition from nuclear 
debris injected into the stratosphere. 29 According to this model the maximum 
annual surface deposition of 90 Sr in the 30 to 50° N latitude band for a 1-MCi 
injection into the lower polar stratosphere (9 to 17 km altitude) would be 
expected to vary between 250 and 400 kCi. For a 1-MCi injection into the upper 
polar stratosphere (17 to 50 km altitude), the maximum annual deposition could 
be expected to vary between 50 and 170 kCi. The cloud from a 1-Mt burst in the 
latitude band 30 to 90° N can be expected to stabilize in the lower polar 
stratosphere, whereas a 10-Mt burst in this region can be expected to stabilize in 
the upper polar stratosphere. Accordingly we have based our estimates on an 
intermediate value of 200 kCi of 90 Sr deposited in one year in the 30 to 50° N 
latitude band per megacurie injected into the stratosphere. It can be readily 
shown that an annual deposition of 1 kCi in the 30 to 50° N latitude band is 
equivalent to a deposition rate of 1.7 X 10 9 /iCi/m 2 /hr. 

An apparent deposition velocity of 40 m/hr has been determined empirically 
from the observed monthly deposition rates and average surface-air concentra- 
tions of 90 Sr in the Northern Hemisphere. 45 An apparent deposition velocity of 
40 m/hr has also been determined on the basis of quarterly deposition rates and 
average surface-air concentrations from U. S. stations alone. 46 A deposition 
velocity of 40 m/hr. together with these assumptions regarding the deposition 
rate of stratospheric debris, leads to an estimate of 8.5 X 10~ 9 jdCi/m 3 for the 
average concentration of 9 Sr in surface air during any 12-month period closely 



RADIONUCLIDE BODY BURDENS 157 

following the injection of 1 MCi into the stratosphere. For present purposes we 
can simply round this off to 1 X 10 8 ^tCi/m 3 , which is the value we have 
assumed for all the nuclides of interest. 

The assumption that 10 8 /^Ci/m 3 is the average surface-air concentration in 
the 30 to 50° N latitude band following the injection of 1 MCi into the 
stratosphere is consistent with measurements reported by Thomas etal. 14 
Table 17 shows ground-level air concentrations measured at Richland, Wash. 
(46° N). The table compares the spring concentration maxima measured in 1963 



Table 17 

RELATION BETWEEN GROUND-LEVEL AIR CONCENTRATION AND 
STRATOSPHERIC BURDEN AT RICHLAND, WASH. (46°N), IN 1963 14 

















Ratio, 




Spring 


concentration maxima 


Stratosph 


eric burden. 


MCi/m 


Nuclide 


dis/min/10 b ft' 


^Ci/m' 


MCi 


MCi 


Mn 


1.4 x 


io 4 


2.2 


x 10" 7 


5 7 


x 10 1 


3.9 x 10^ 


106 Ru 


7.0 x 


io 4 


1.1 


x 10^ 


2.1 


x 10 2 


5.3 x 10^ 


125 Sb 


9.0 x 


io 3 


1.4 


x IO" 7 


3.3 


x IO 1 


4.4 x 10^ 


137 Cs 


7 5 x 


io 3 


1.2 


x 10" 7 


1.5 


x IO 1 


8.2 x IO" 9 


144„ 

Cc 


1.0 x 


io 5 


1.6 


x 10" 6 


3.6 


x IO 2 


4.5 x IO" 9 



with the megacuries injected into the stratosphere in the 1961 — 1962 series. As 
mentioned previously, the total fission yield of the 1961 — 1962 atmospheric 
detonations was about 100 Mt. The ratio between the air concentration in 
microcuries per cubic meter and the stratospheric burden in megacuries varied 
between 4 X IO 9 and 8 X 10 9 ; if the ratio were calculated with the average 
concentration for the year, it would of course be smaller. A large fraction of the 
stratospheric burden from the 1961 — 1962 test series was injected into the upper 
stratospheric compartment. By assuming a higher value of 10 8 for the ratio of 
air concentration to stratospheric burden, we allow for injections into the lower 
stratospheric compartment, from which initial deposition rates will be greater. 

Deposition of Nuclides on Vegetation 

To estimate the dosage that could result from the continuous deposition of 
radionuclides on vegetation, we estimated the steady-state deposition of particles 
on forage, F e q, as the quotient of the deposition rate, R, and the rate of loss by 
weathering, X^ : 

F eq=r" (3) 



158 



NG ANDTEWES 



Since the deposition rate, R, is related to the air concentration, L, bv the 
deposition velocity, V g , 



R = V g L 



(4) 



the equilibrium deposition on forage can be expressed in terms of the air 
concentration: 



eq 



V g L 

*m 



(5) 



The food contamination and dosage from the continuous deposition of 
nuclides from the stratosphere were estimated from equilibrium depositions, 
F e q, determined as outlined previously. The deposition velocity, V g , was 
assumed to be 40 m/hr, and the rate of loss by weathering, X\^, was assumed to 
be 0.05 per day, which is equivalent to a half-residence time on forage of 
14 days. 

Forage-Cow-Milk Pathway 

The forage— cow— milk model, as previously described for small particles, 
assumes a UAF of 45 m 2 /day and an initial retention factor of two-thirds. 

Concentrations of Nuclides in Milk 

Table 18 lists the estimated average concentrations for fission products in 
milk from stratospheric deposition during a year closely following the 



Table 18 

ESTIMATED AVERAGE CONCENTRATIONS IN MILK AND MEAT FROM 

THE STRATOSPHERIC DEPOSITION DURING A YEAR CLOSELY 

FOLLOWING THE HYPOTHETICAL ATTACK (FISSION PRODUCTS ONLY) 





cm* 




c. 


neat 






juCi/liter 




MCi/kg 




Ratio of 


Radionuclide 


/iCi/m 


luCi/liter 


juCi/m 


MCi/kg 


Cmeat to <-M 


89 c 
Sr 


3.9(2) 


1.2 (-3) 


6.4 (1) 


1.9 (-4) 


0.2 


90c, 
Sr 


4.9 (2) 


8.6 (-4) 


8.3 (1) 


1.5 (-4) 


0.2 


106 Ru 


5.3 (-1) 


1.1 (-5) 


1.8 (3) 


3.8 (-2) 


3000 


125 Sb 


2.7(0) 


1.4 (-5) 


3.5 (3) 


1.8 (-2) 


1000 


1 37 „ 

Cs 


4.1 (3) 


1.2 (-2) 


4.7 (4) 


1.4 (-1) 


10 


1 44 „ 
Ce 


1.0(1) 


3.0 (-4) 


3.7 (2) 


1.1 (-2) 


30 



*The numerical value in parentheses signifies the exponential power of 10; thus 3.9 (2) 
signifies 3.9 x 10 . 



RADIONUCLIDE BODY BURDENS 159 

hypothetical attack. Table 19 gives the estimates for activation products. The 
nuclides listed are those having half-lives greater than 45 days. The concentra- 
tions are both for unit air concentration and for the estimated average 
concentration for the year. 

Table 19 

ESTIMATED AVERAGE CONCENTRATIONS IN MILK AND MEAT FROM 

THE STRATOSPHERIC DEPOSITION DURING A YEAR CLOSELY 

FOLLOWING THE HYPOTHETICAL ATTACK (ACTIVATION PRODUCTS ONLY) 





Cm - 




c 


* 
meat 






juCi/liter 




/iCi/kg 




Ratio of 


Radionuclide 


juCi/rrf 


juCi/liter 


juCi/m 


MCi/kg 


c meat to C\i 


22 M 

Na 


8.1 (3) 


1.3 (-3) 


6.2 (4) 


8.7 (-3) 


7 


45^ 
Ca 


7.1 (3) 


2.3 (-3) 


2.2 (3) 


7.1 (-4) 


0.3 


54 A . 
Mn 


5.3 (0) 


6.3 (-6) 


5.0(2) 


6.0 (-4) 


100 


55,-. 
Fe 


2.2(1) 


9.9 (-5) 


6.1 (3) 


2.8 (-2) 


300 


5 7„ 
Co 


2.1 (2) 


1.5 (-4) 


1.4 (3) 


1.0 (-3) 


7 


58^ 

Co 


1.8(2) 


4.4 (-5) 


8.4(2) 


2.0 (-4) 


4 


Co 


2.2 (2) 


1.2 (-5) 


1.8 (3) 


9.6 (-6) 


0.8 


65~ 
Zn 


5.2(3) 


1.1 (-4) 


1.6 (4) 


3.5 (-4) 


3 


1 1 m . 
Ag 


2.6(3) 


5.7 (-6) 


6.4 (3) 


1.4(-5) 


2 


1 34„ 
Cs 


4.0(3) 


5.6 (-4) 


4.5 (4) 


6.3 (-3) 


10 



*The numerical value in parentheses signifies the exponential power of 10; thus 8.1 (3) 
signifies 8.1 x 10' . 



Estimated Dosage via Milk 

Tables 20 and 21 present estimates of the average dose rate via milk to adult 
whole body and bone from the nuclides depositing from the stratosphere during 
a year closely following the hypothetical attack. Fission products are considered 
in Table 20 and activation products in Table 21. The rates of ingestion were 
calculated assuming milk consumption of 1 liter/day. The dose rates to whole 
body and bone assume that the concentration of the nuclide in tissue has 
reached a steady state with respect to the constant rate of ingestion.* The total 
dose rate from fission products (Table 20) is about 1 rad/year in the whole body 
and about 6 rads/year in bone. It comes as no surprise that 90 Sr, l 37 Cs, and, to 
a lesser extent, 89 Sr, contribute most to the dose rate from fission products. 



The dose commitment (rads) from a given nuclide would be estimated as the product 
of the dose rate (rads/year) and the mean residence time of the nuclide in the stratosphere 
(year). 



160 



NG ANDTEWES 



Table 20 

ESTIMATED AVERAGE DOSE RATE VIA MILK TO WHOLE BODY AND BONE 

FROM FISSION PRODUCTS DEPOSITING FROM THE STRATOSPHERE 

DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK 





Rate of ingestion 


Radionuclide 


/iCi/year 


89 c 
Sr 


4.2 (-1) 


90 c 
Sr 


3.2(-l) 


106 Ru 


4.1 (-3) 


125 Sb 


4.9 (-3) 


1 37„ 

Cs 


4.4 (0) 


144,, 

Ce 


1.1 (-D 



Dose rate,* rads/vear 



Whole body 


Bone 


3.6 (-3) 


0.028 


0.62 


5.4 


1 (-4) 


4 (-4) 


2 (-6) 


5 (-6) 


0.29 


0.29 


3 (-6) 


1 (-5) 



Total dose rate 



0.91 



5.7 



The numerical value in parentheses signifies the exponential power o\ 10; thu^ 4.2 (-1) 



signifies 4.2 x 10 



Table 21 

ESTIMATED AVERAGE DOSE RATE VIA MILK TO WHOLE BODY AND BONE 
FROM ACTIVATION PRODUCTS DEPOSITING FROM THE STRATOSPHERE 
DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK 



Radionuclide 



Rate of ingestion, 

juCi/vear 



Dose rate,* mrads/year 



Whole body 


Bone 


7.6 


7.6 


7.2 


72 


4 (-3) 


2 (-2) 


1 (-2) 


2 (-2) 


3 (-2) 


2 (-2) 


6 (-2) 


5 (-2) 


5 (-3) 


3 (-3) 


0.3 


0.47 


0.16 


0.26 


23 


23 



22 



54 



57 



Na 
Ca 
Mn 
Fe 
Co 

Co 
Co 



65 



Zn 
10m 



Ag 



h Cs 



4.1 (-1) 

8.2 (-1) 

2.3 (-3) 
3.6 (-2) 
5.3 (-2) 

1.6 (-2) 
4.2 (-4) 
4.2 (-2) 
2.1 (-3) 
2.1 (-1) 



Total dose rate 



38 



100 



*The numerical value in parentheses signifies the exponential power ot 10: thus 4.1 (— 1) 
signifies 4.1 x 10 . 



RADIONUCLIDE BODY BURDENS 161 

A comparison of Tables 20 and 21 reveals that the dose rate to the whole 
body from fission products would exceed that from activation products by 
about a factor of 20; the dose rate to bone from fission products would exceed 
that from activation products by about a factor of 50. The activation products 
of Table 21 which would contribute most to the dosage via milk are the 
neutron-activation products of soil and rock, " Na, 3 Ca, and Cs. The dose 
rates listed in Table 21 are expressed in millirad units. Activation products of 
device origin would contribute relatively little to the total dose rate. 

Plant-Herbivore-Meat Pathway 

The estimates via meat, like those via milk, were made as previously 
described for small particles, assuming a UAF of 45 m /day and an initial 
retention factor of two-thirds. 

Concentration of Nuclides in Meat 

Tables 18 (for fission products) and 1 () (for actuation products) list the 
estimated average concentrations in meat from stratospheric deposition during a 
year closely following the hypothetical attack. The nuclides listed have half-lives 
greater than 45 days. The concentrations arc both for unit air concentration and 
for the estimated average concentration for the year. The meat-to-milk ratios of 
average concentrations, given in the last column of these tables, suggest that, 
except for isotopes of calcium and strontium, the nuclide concentrations in meat 
would be about the same as. or greater than, those in milk. According to these 
calculations, the average concentration of Ru and ' ' Sb in meat would 

exceed their average concentration in milk by three orders of magnitude. The 
average concentration of Fe in mc.it would exceed its average concentration in 
milk by more than a factor of LOO. 

Estimated Dosage via Meat 

Tables 2 2 and 23 present the estimates of the average dose rate via meat to 
the adult whole body and bone from the nuclides depositing from the 
stratosphere during a year closely following the hypothetical attack. Fission 
products are considered in Table 22 and activation products in Table 23. The 
rate of ingestion was calculated assuming meat consumption at the rate of 
300 g/day. Again Sr and l 7 Cs make major contributions to the total dose 
rate via meat; in addition, Ru makes a substantial contribution. As 

mentioned earlier, the input parameters required for ruthenium isotopes via this 
pathway are open to question. The dose rate to the whole body from fission 
products via meat totals 1.2 rads/year, whereas that to bone totals 1.8 rads/year. 
The dose estimates from activation products are again less by about an order of 
magnitude. The neutron-activation products singled out in Table 2 3 include 
Na, Ca, and ' Cs, the same nuclides of environmental origin previously 



162 



NG ANDTEWES 



Table 22 

ESTIMATED AVERAGE DOSE RATE VIA MEAT TO WHOLE BODY AND 

BONE FROM FISSION PRODUCTS DEPOSITING FROM THE STRATOSPHERE 

DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK 





Rate of ingestion,* 


Dose rate 


* radsA 


ear 










Radionuclide 


uCi/year 


Whole body 




Bone 


89 c 
Sr 


2.1 (-2) 


1.8 (-4) 




1.4(-3) 


90„ 

Sr 


1.6 (-2) 


0.03 




0.27 


1 06^ 
Ru 


4.2(0) 


0.12 




0.45 


1 25 cu 

Sb 


2.0 (0) 


8 (-4) 




2 (-3) 


137 Cs 


1.5 (1) 


1.0 




1.0 


144 Ce 


1.2(0) 


3 (-5) 




1 (-4) 



Total dose rate 



1.2 



*The numerical value in parentheses signifies the exponential power of 10; thus 2.1 ( — 2) 
signifies 2.1 x 10 . 



Table 2 3 

ESTIMATED AVERAGE DOSE RATE VIA MEAT TO WHOLE BODY AND BONE 
FROM ACTIVATION PRODUCTS DEPOSITING FROM THE STRATOSPHERE 
DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK 



Radionuclide 



Rate of ingestion, 
uCi/vear 



Dose rate,* mrads/vear 



Whole bodv 



Bone 



55 



Na 

'Ca 



Mn 
Fe 



Co 



60 



Co 
Co 



Zn 

l l om 



\Z 



Cs 



9.6 (-1) 
7.8 (-2) 
6.6 (-2) 
3.1 (0) 

1.1 (-D 

2.2 (-2) 
1.1 (-3) 

3.8 (-2) 
1.6 (-3) 

6.9 (-1) 



17 

0.68 

0.11 

0.93 

0.07 

0.08 
0.01 
0.25 
0.1 

77 



17 
6.8 
0.5 
1.4 
0.05 

0.06 
0.01 
0.43 
0.2 

77 



Total dose rate 



96 



100 



: The numerical value in parentheses signifies the exponential power of 10; thus 9.6 (— 1) 



signifies 9.6 x 10 



RADIONUCLIDE BODY BURDENS 163 

singled out via milk. In addition, ' " Fe, of device origin, would make a small 
contribution. 

Summary of Dosage Estimates 

Table 24 summarizes the dosage estimates from stratospheric deposition. 
The table shows the dominant role of fission products, whose contributions to 
the dosage exceed those of activation products by more than a factor of 10. The 



Table 24 

SUMMARY OF SOURCE CONTRIBUTIONS TO THE ESTIMATED AVERAGE 

DOSE RATES VIA MILK AND MEAT FROM STRATOSPHERIC DEPOSITION 

DURING A YEAR CLOSELY FOLLOWING THE HYPOTHETICAL ATTACK 





Milk pathway 


rad 


*/year 


Meat pathway 


radsA 


ear 


Source 


Whole body 




Bone 


Whole body 




Bone 


Fission 

Neutron activation 


0.91 
0.038 




5.7 
0.10 


1.2 

0.096 




1.8 

0.10 



Total 0.95 5.8 1.3 1.9 



tabic also shows that the dose rates via the two routes (via milk and via meat) 
would not differ greatly. Thus, for continuous deposition extending in time, the 
meat and milk pathways would be more comparable in importance. For the 
single discrete depositions previously considered, the milk pathway assumes a far 
greater importance. 

Interpretations of the Estimates 

Before discussing the dosage estimates from nuclides initially depositing 
from the stratosphere, let us consider briefly the validity of the model for 
chronic contamination. This model involves the derivation of a proportionality 
factor between the average nuclide concentration in milk or meat and the 
average nuclide concentration in surface air. The relation of air concentration of 
a nuclide to \ook\ contamination obviously invokes factors relating to 
plant-retention characteristics, the local environment, and agricultural feeding 
practices. Wilson 4 ' developed an ecologically based quantitative model ot the 
transport o\ ' 3 Cs from fallout to milk. This model can predict to a high degree 
of precision the mean quarterly levels oi ' Cs in milk from the mean surface 
concentrations in air. The linear correlation between mean quarterly Cs 

levels in milk and mean surface-air concentrations durum the growing season tor 



164 NGANDTEWES 

various milksheds across the nation was characterized by a value of 710 pCi/liter 
in milk per picocune per cubic meter in surface air. This particular correlation 
was associated with dry-lot feeding. The Seattle milkshed exhibited a different 
correlation, which by our calculations is characterized by a value of 
4100 pCi/liter in milk per picocune per cubic meter in surface air. The response 
of the Seattle milkshed was thought to be characteristic of pasture feeding. Our 
model assumes that the animals providing the milk and the meat are 
continuously on pasture. The " Cs concentration in milk listed in Table 18 is 
equivalent to 4100 pCi/liter per picocurie per cubic meter in surface air. This close 
correspondence to the Seattle value obtained by Wilson is. of course, fortuitous. 
An inspection of milk concentrations and surface-air concentrations of 137 Cs 
and 90 Sr measured from the middle of 1963 at Ispra, Italy (as reported in the 
HASL series of reports from the Health and Safety Laboratory. U, S. Atomic 
Energy Commission ), indicates that the correlation between " Cs concentra- 
tions in milk and air would be about 5200 (pCi/liter)/(pCi/m ). For Sr the 
correlation at Ispra would be about 960 (pCi/liter)/(pCi/m ). When the 
concentrations of 90 Sr in milk from the Seattle milkshed 49 were compared with 
the surface-air levels over Seattle. the correlation was estimated to be 620 
GuCi/liter)/(juCi/m 3 ). The concentration of ' )0 Sr listed in Table 18 is 490 
(juCi/liter)/(piCi/m 3 ). If we assume that pasture feeding was the dominant 
practice at Ispra and Seattle, the values listed in Table 18 for the concentrations 
of ] 3 7 Cs and 9 ° Sr in milk appear to be reasonable. 

Since field data on concentrations of nuclides in meat are far less abundant 
than those in milk, particularly for 90 Sr, we simply compared the predicted and 
observed ratios of the concentration in meat to that in milk. The concentration 
of stable strontium per gram of calcium in meat is about twice that in milk. 50 
The concentration of 90 Sr per gram of calcium in meat also was found to be 
twice that in milk in the United Kingdom diet of 1963 and 1964 (Refs. 51 and 
5 2). On the basis of the stable calcium content of milk and meat (1.3 g Ca/liter 
and 0.1 g Ca/kg. respectively 6 ). the ratio of the average concentration of Sr in 
meat to that in milk could be expected to be 0.15. (We assumed that the 90 Sr 
burdens of 1963 and 1964 are largely attributed to direct contamination.) The 
ratio can be expected to vary with geographical location. Thus the ratio of the 
average yearly concentration of 90 Sr in meat to that in milk in the Danish diet 
from 1962 to 1964 varied from 0.20 to 0.26 (Refs. 53 — 55). After examining the 
tri-city data on 90 Sr concentration in foods from 1962 to 1964 (from the HASL 
reports 48 ), we estimated the increments of the burdens that were associated 
with recent deposition. The estimated ratio of the average concentration of Sr 
attributable to direct contamination in meat to that in milk was about 0.11 to 
0.14 in the San Francisco and Chicago diets. The concentration of °Sr reported 
for meat in the Xew York diet was relatively insensitive to fresh contamination, 
and the meat-to-milk ratio was less than 0.05. The ratio listed in Table 18, 0.2, is 
within the range reported. 



RADIONUCLIDE BODY BURDENS 165 

Meat and milk together have been the main dietary sources of 137 Cs. The 
concentration of 137 Cs in meat could be expected to exceed that in milk; e.g., 
the correlation between the 137 Cs contents in beef and milk in Sweden from 
1962 to 1966 is characterized by a concentration ratio (picocurie per kilogram 
of meat to picocurie per liter of milk) averaging 4.3 (Ref. 56). The ratio of the 
average yearly concentration of 137 Cs in meat to that in milk in the United 
Kingdom from 1961 to 1964 varied from 3.2 to 5.3 (Ref. 52). The ratio in 
Denmark was 5.8 in 1963 (Ref. 54) and 5.3 in 1964 (Ref. 55). The meat-to-milk 
ratio of 137 Cs listed in Table 18 is 10. The predicted concentration of 90 Sr and 
7 Cs in meat appears to be acceptable in view of the wide variation that could 
be expected. Thus the average concentration of ] 37 Cs in beef sampled at various 
slaughterhouses in Norway from 1965 to 1967, ranged from 120 to 1700 pCi/kg 
(Ref. 57). The average concentration in mutton ranged from 5 20 to 
4800 pCi/kg. This variation points out the important role of differences in local 
environmental factors and feeding practices. 

Let us now consider the dosage estimates presented in Tables 20 and 23 for 
the nuclides depositing from the stratosphere. If both the concentrations of the 
nuclides in milk and meat and the ingestion rates were as we have supposed, we 
could accept these estimates at face value. The dose rates shown in these tables 
for the year closely following the initial injection of the nuclides into the 
stratosphere, combined with the decreasing dose rates that would be associated 
with nuclide deposition in succeeding years, would constitute a long-term 
internal dose commitment. This dose commitment would make a substantial 
contribution to the dose commitment for the individual who was adequately 
protected from the gamma field in the few weeks immediately following an 
attack and who also avoided contaminated foods during this period. 

It is interesting to compare the estimated yearly dose rates from fission 
products via milk (Table 20) with the corresponding estimated doses from local 
and tropospheric deposition at early times (Table 7). The total yearly dose rate 
to the whole body and bone from stratospheric deposition is somewhat less than 
the total dose commitment to these organs from the 10 8 kt/m 2 deposition at 
early times. However, the yearly dose rate from stratospheric deposition, which 
is attributable to 90 Sr and 137 Cs, is comparable to the dose from the early 
deposition of these nuclides. This simple comparison points out the significance 
of the stratospheric compartments for these long-lived nuclides. The initial 
deposition rate from the stratosphere, and hence the initial average dose rate, 
may be either greater or less than our estimate. But, since the residence time of 
stratospheric debris is measured in months or vears rather than in decades, 
essentially all the stratospheric burden of 90 Sr and 137 Cs would reach ground 
level where it could then contribute to the internal dose commitment before 
radioactive decay. 

It is also interesting to compare the external and internal dosages that would 
be associated with long-term deposition. The internal and external dosages 



166 NGANDTEWES 

resulting from ] 37 Cs deposition are estimated to be equal. 58 ' 59 Since over 80% 
of the activity injected into the lower and upper polar stratospheric compart- 
ments can be expected to deposit in the hemisphere of injection, 2 9 the average 
cumulative deposition of 137 Cs in the Northern Hemisphere following the 
hypothetical injection of 2000 Ait of fission products into this region of the 
stratosphere would be about 1.2 [dCi/m 2 . The average deposition in the 30 to 
50° N latitude band would be about twice as great, 29 or 2A [dCi/m 2 . A 
dose-conversion factor of 0.04 (rad/year)/(/iCi/m 2 ) coupled with a mean life of 
44 years leads to an external dose commitment of 4.2 rads from 137 Cs 
(Ref. 5 9). The actual dose to the gonads and bone marrow would be about 
one-fifth as great, or about 0.85 rad, because of shielding by building structures 
and screening by the human body. 59 

The internal dose commitment to these tissues from stratospheric 137 Cs, 
assuming milk consumption at the rate of 1 liter/day, is estimated according to 
our present scheme as the product of the dose rate, 0.29 rad/year (Table 20), 
and the mean life of J 37 Cs in the stratosphere. The half-residence time of debris 
is estimated to be 5 months in the lower polar stratosphere and about 2 years in 
the upper polar stratosphere. 29 If we assume a half-residence time of 1 year, the 
dose commitment from 7 Cs via milk would be 0.42 rad. This seems to be a 
reasonable value in relation to the total estimated external or internal dose 
commitment of 0.84 rad since milk is known to contribute a substantial fraction 
of the dietary l 3 ' Cs and since direct contamination is regarded as the 
predominant pathway for the entry of 137 Cs into foods. 60 Bear in mind that 
this analysis is confined to the contamination of food as a result of direct 
contamination of vegetation. For Sr, uptake from soil over the long term can 
be expected to make a major contribution to the contamination of terrestrial 
foods. 60 

Although the external and internal dosages from Cs deposition would be 
comparable, it is important to note that initially the internal dose rate will 
exceed the external dose rate. The cumulative ground deposition of l 37 Cs from 
stratospheric deposition would be about 1.0/iCi/m 2 at the end of the year 
following the hypothetical attack. The gamma field associated with such a 
deposition of 137 Cs is 0.04 rad/year, which is considerably less than the 
estimated initial average dose rate via milk (0.29 rad/year) shown in Table 20. If 
we consider the other dietarv sources of 7 Cs and at the same time make more 
reasonable assumptions regarding average rates of ingestion, the internal dose 
rate would still initially exceed the external dose rate to the degree shown above 
or to an even greater degree. 

Evaluation of Risk 

This analysis was undertaken to estimate potential levels of food contamina- 
tion and dosage to individuals and is not intended to evaluate risk from radiation 
exposure either to individuals or to populations. If the dosage estimates are to be 



RADIONUCLIDE BODY BURDENS 167 

used for risk evaluation, we must take into account two factors: how the dose 
from a given nuclide is spatially distributed among tissues and the relative 
susceptibility of the cell types involved. 61 The 90 Sr, for example, concentrates 
in bone. The risk of developing malignant diseases, which is associated with 90 Sr 
deposition, is a consequence of the dosages delivered to the cells that line bone 
surfaces and to bone marrow. The dose delivered to the cells that line bone 
surfaces has been estimated to be about one-half and that to bone marrow about 
one-fourth the mean dose delivered to bone. The concentration of 90 Sr in 
bone is so very much greater than that in other tissues that the estimated 
whole-body dose would not be representative of the dose to the gonads or to 
other soft tissues. Thus the gonad dose from Sr is usually neglected. On the 
other hand. ~ Cs is distributed more or less uniformly; thus the dose to the 
gonads, bone marrow, and cells that line bone surfaces would be comparable to 



SUMMARY 

A method was developed for predicting the internal dose that could result 
when radionuclides arc released to the biosphere and deposited on agricultural 
land. By means of this analysis, we can identify the nuclides that could 
contribute most to the internal dose. The method was used to estimate the 
potential levels of food contamination au^\ the dose commitment to man as a 
consequence of a nuclear attack. Neutron-activation products as well as fission 
products were considered as source terms. ()t the many nuclides considered. 
relatively few were singled out as critical. It has been recognized many times that 
the potential dosage to a child's thyroid from isotopes of iodine via milk would 
be the principal internal hazard in the immediate postattack period. Thus, if 
normally functioning cows were grazing on pasture contaminated by unfrac- 
tionated fission products deposited as small particles, children consuming the 
milk could receive thyroid dosages exceeding the open-field gamma dose by two 
orders of magnitude. The dosages to the whole body and bone would not exceed 
the external dose. Neutron-activation products ot the environment would not be 
expected to contribute more than one-tenth ot the total dose to the whole body 
and bone. Actuation products of device origin would contribute little to the 
internal dose via the terrestrial pathways considered. Dosages attributable to a 
comparable deposition of large particles (such as are characteristic of close-in 
fallout) would be lower by a factor of 10 or more. As we might expect, the meat 
pathway would be unimportant compared with the milk pathway following 
single depositions on vegetation. 

Preliminary estimates were made for the average dose rates that could result 
from the initial rate of deposition of the nuclides injected into the stratosphere. 
To no one's surprise, 90 Sr and 137 Cs would predominate among the 
contributors to the total dose rate. In this situation, where there is continuous 



168 NGANDTEWES 

deposition extending in time, the meat pathway would be more comparable to 
the milk pathway in importance than was the case for single deposition. 
Neutron-activation products, particularly those of device origin, would not 
contribute substantially to the dose rates from stratospheric deposition. 
Comparison of the estimated dose rates from the stratospheric deposition of 
90 Sr and 137 Cs w : ith the dosages from the single deposition points out the 
important role of the stratosphere as a reservoir from which, sooner or later, 
essentially all 90 Sr and 137 Cs is transported to ground level, where it can 
deposit on vegetation and soil and contribute to the internal dose commitment 
before radioactive decay. The internal dose commitment from this source would 
constitute a residual long-term burden, which would be a major fraction of the 
total burden from these nuclides. 



ACKNOWLEDGMENTS 

This work was performed under the auspices of the U. S. Atomic Energy 
Commission. 

We are pleased to acknowledge helpful discussions with Daniel W. Wilson, 
Fallout Studies Branch, Division of Biologv and Medicine, U. S. Atomic Energv 
Commission, and with the following investigators from the Lawrence Radiation 
Laboratory, Livermore: Kendall R. Peterson. K Division, and Arthur R. 
Tamplin, Bio-Medical Division. We also wish to thank R. Scott Russell, 
Agricultural Research Council. Letcombe Laboratory, Wantage, Berkshire. 
United Kingdom, for helpful comments and suggestions. We gratefullv acknowl- 
edge the assistance provided by C. Ann Burton and Stanley E. Thompson in 
updating the Handbook parameters and making them available, by Michael W. 
Pratt and Gary A. Kortan in programming and computation, by Yvonne Ricker 
and Thelma Smith in data handling and processing, and by Valeska Evertsbusch 
in editing the manuscript. 

We are grateful to J. P. Witherspoon and F. G. Taylor, Jr., 33 and to J. E. 
Johnson and A. I. Lovaas ' 5 for making results of their studies available to us 



in advance of formal publication. 



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RADIONUCLIDE BODY BURDENS 169 

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11. C. F. Miller. Fallout and Radiological Countermeasures. Volume I. Report AD-410522, 
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14. C. W. Thomas. J. A. Young, N. A. Wogman, and R. W. Perkins, The Measurement ami 
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15. A. \\ . Klement, Radioactive Fallout Phenomena and Mechanisms, Health Pbys., 11: 
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16. M. Eisenbud, Environmental Radioactivity, p. 307. McGraw-Hill Book Company, Inc.. 
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17.11. A. Tewes, Results oi the Schooner Excavation Experiment, in Engineering with 
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19. R. M. Lessler and F. W. Guy, Neutron-Induced Activity in Earth and Seawater from 
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Laboratory, Livermore, Apr. 9, 1965. 



170 NGANDTEWES 

20. Y. C. Ng, Neutron Activation of the Terrestrial Environment as a Result of Underground 
Nuclear Explosions, USAEC Report UCRL-14249, Lawrence Radiation Laboratory, 
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21. O. I. Leipunsky, Radiation Hazards from Clean Hydrogen Bomb and Fission Atomic 
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22. W. F. Libby, Radioactive Fallout, Proc. Sat. Acad. Sci. U. S. A., 44: 800-820(1958). 

23. R. M. Lessler, Reduction of Radioactivity Produced by Nuclear Explosives, in 
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24. J. R. Martin and J.J. Koranda, The Importance of Tritium in the Civil-Defense Context, 
this volume. 

25. J. A. Miskel, Characteristics of Radioactivity Produced by Nuclear Explosives, 
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versity of California and AEC San Francisco Operations Office. 

26. H. A. Tewes, Radioactivity from Nuclear Excavation Explosives, USAEC Report 
UCRL-71323, Lawrence Radiation Laboratory, Livermore, Oct. 23, 1968. 

27. G. V. LeRoy, Re-examination of NCRP Report No. 29, in Radiological Protection of 
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28. A. R. Tamplin, Prediction of the Maximum Dosage to Man from the Fallout of Nuclear 
Devices. I. Estimation of the Maximum Contamination of Agricultural Land, USAEC 
Report UCRL-50163(Pt. 1). Lawrence Radiation Laboratory, Livermore, Jan. 3, 1967. 

29. K. R. Peterson, An Empirical Model for Estimating World-Wide Deposition from 
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30. T. V. Crawford, A Computer Program for Calculating the Atmospheric Dispersion of 
Large Clouds. USAEC Report UCRL-50179. Lawrence Radiation Laboratory, Liver- 
more, Nov. 23. 1966. 

31. A. C. Chamberlain, Interception and Retention of Radioactive Aerosols by Vegetation, 
Atmos. Environ.. 4: 57-78 (1970). 

32. S. E. Thompson, Effective Half-Life of Fallout Radionuclides on Plants with Special 
Emphasis on Iodine-131, USAEC Report UCRL-12388, Lawrence Radiation Labora- 
tory. Livermore. Jan. 29. 1965. 

33. J. P. Witherspoon and F. G. Taylor, Jr.. Interception and Retention of a Simulated 
Fallout by Agricultural Plants, Health Phys., 19: 493-499 (1970). 

34. J. E. Johnson and A. I. Lovaas, Retention of Near-In Fallout by Field Crops and 
Livestock, Report AD-715423, Colorado State University, 1970. 

35. A. I. Lovaas and J. E. Johnson, Retention of Near-In Fallout by Crops, this volume. 

36. C. F. Miller, The Retention by Foliage of Silicate Particles Ejected from the Volcano 
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3 7. J. J. Koranda, Agricultural Factors Affecting the Daily Intake of Fresh Fallout by Dairy 

Cows, USAEC Report UCRL-12479, Lawrence Radiation Laboratory, Livermore, 

xMar. 19, 1965. 
3 8. G. D. Potter, D. R. Mclntyre, and D. Pomeroy, Transport of Fallout Radionuclides in 

the Grass-to-Milk Food Chain Studied with a Germanium Lithium-Drifted Detector, 

Health Phys., 16: 297-300(1969). 



RADIONUCLIDE BODY BURDENS 171 

39. G. D. Potter, G. M. Vattuone, and D. R. Mclntyre, Fate of Fallout Ingested by Dairy 
Cows, this volume. 

40. G. D. Potter, Lawrence Radiation Laboratory, Livermore, personal communication, 
1970. 

41. R. J. Chertok and S. Lake, Fate of Fallout Ingested by Swine and Beagles, this volume. 

42. W. C. Hanson, D. G. Watson, and R. W. Perkins, Concentration and Retention of Fallout 
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43. C. E. Jenkins and W. C. Hanson, Radionuclide Distribution in the Alaskan Arctic- 
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44. C. F. Miller and P. D. LaRiviere. Introduction to Long-Term Biological Effects of 
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45. M. T. Kleinman and H. L. Volchok. Radionuclide Concentrations in Surface Air: Direct 
Relationship to Global Fallout, Science, 166: 376-377 (1969). 

46. K. R. Peterson, Lawrence Radiation Laboratory, Livermore, personal communication. 
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47. D. W. Wilson, G. M. Ward, and J. I . Johnson. A Quantitative Model of the Transport o\ 

Cs from Fall-out to Milk, in Environmental Contamination by Radioactive Materials, 
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48. Fallout Program Quarterly Summary Reports, L. S. Atomic Energy Commission Health 
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49. Radiological Health Data and Reports, published monthly by the U.S. Public Health 
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50. Great Britain .Agricultural Research Council, Strontium-90 in Human Diet in the United 
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51. Agricultural Research Council. Annual Report. 1963 L964, British Report ARCRL-12, 
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52. Agricultural Research Council, Annual Report. 1 964 L965, British Report ARCRL-14, 
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53. A. Aarkrog, J. Lippcrt. and J. Petersen, Environmental Radioactivity in Denmark in 
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54. A. Aarkrog and J. Lippert, Environmental Radioactivity in Denmark in 1963, Danish 
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55. A. Aarkrog and J. Lippert. Environmental Radioactivity in Denmark in 1964, Danish 
Report No. 107, 1965. 

56. Report of the United Nations Scientific Committee on the Effects ot .Atomic Radiation, 
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57. B. Undcrdal, Measurement of Cs in Meat from Different Species, 1965 — 1907, Nord. 
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59. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, 
General Assembly Official Records. Twenty-fourth Session, Supplement No. 13 
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60. R. S. Bruce and R. S. Russell, Agricultural Aspects of Acute and Chronic Contamination 
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172 NGANDTEWES 

Proceedings, Vienna, Mar. 24—28, 1969, pp. 79—89, International Atomic Energy 
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61. International Commission on Radiological Protection, Radio sensitivity and Spatial 
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62. Report of the United Nations Scientific Committee on the Effects of Atomic Radiation, 
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63. L. L. Schwartz, Lawrence Radiation Laboratory, Livermore, personal communication, 
1970. 

64. H. W. Feely and F. Bazan, Stratospheric Distribution of Nuclear Debris in 1962, 1963, 
and 1964, in Radioactive Fallout from Nuclear Weapons Tests, Germantown, Md., 
Nov. 3-6, 1964, A. W. Klement, Jr. (Ed.), AEC Symposium Series, No. 5 (CONF-765), 
pp. 301-322, 1965. 

65. G. H. Higgins, Calculation of Radiation Fields from Fallout, USAEC Report 
UCID-4539, Lawrence Radiation Laboratorv, Jan. 25, 1963. 



RETENTION OF SIMULATED FALLOUT 
BY SHEEP AND CATTLE 



JAMES E. JOHNSON and ARVIN I. LOVAAS 

Department of Animal Science, Colorado State University, Fort Collins, Colorado 



ABSTRACT 

The initial retention of 88- to 175-ju or 175- to 350-ju near-in fallout-simulant sand on the 
backs of cattle averaged 50%. This was independent of mass loading up to 100 g/m . The 
retention half-time of simulant deposited on the animals' backs averaged 9 days for cattle 
kept under feedlot conditions and 2 days for cattle kept under pasture conditions. 

The fecal excretion of simulant sand given to sheep and cattle could be described by 
single exponential functions. The mean lifetime (1.44Ty 2 ) of material in the gut averaged 
1.1 days in sheep and 4.8 days in cattle. 

The beta-particle radiation dose to grazing and feedlot animals from near-in 
fallout would be principally due to retention of particulates on the body and 
their passage through the gut. 



RETENTION ON THE SURFACE OF ANIMALS 

Near-in fallout-simulant sand was spread as an aerosol over 26 Hereford and 
Angus cattle by means of a blower. The sand, which was labeled with Lu for 
identification by gamma-ray spectrometry, was in the particle range either 88 to 
175 /J or 175 to 350 [i. The aerosol was generated at a height sufficient to 
guarantee terminal velocity before deposition. Initial retention was determined 
by comparison with deposition on disk impactors. A 0.6-cm-thick 7.5-cm- 
diameter Nal(Tl) scintillation crystal was used for counting. 

The initial retention, as well as the retention as a function of time, was 
dependent on the location on the surface of the animal's back. The mean initial 
retention of all the sites monitored was about 50% for studies using the 88- to 
175-/J sand. For the 175- to 350-jU size the mean initial retention was also near 
50%. 



173 



174 



JOHNSON AND LOVAAS 



Figure 1 shows the retention vs. time at four different locations for one cow. 
Loss is reasonably rapid for the convex locations and is minimal for the flat or 
concave locations. 

Retention was also strongly dependent on the activity of the animals. 
Figure 2 compares retention on animals kept under feedlot conditions with that 
on animals allowed the greater mobility of pasture conditions. The retention 
half-time for pastured animals was less than 2 days but was greater than 9 days 
for animals kept under feedlot conditions. The loss rate for the coarse sand was 
slightly greater than for the fine sand. 

In summary, the greatest beta-radiation skin dose would be to the region 
between the hook bones, and, since most U. S. cattle are kept under pasture 
conditions, a retention half-time of 2 days should probably be used in the dose 
calculation. 



100 




6 8 

DAY OF EXPERIMENT 



14 



Fig. 1 Typical retention of 88- to 175-/i sand at four locations on the back of 
cow 712: curve 2, between tuber coxa; curve 4, between shoulders; curve 6, 
paralumbar fossa? and curve 8, over shoulder joint. 



RETENTION OF SIMULATED FALLOUT 



175 



100 



10 




Feedlot 



Pasture 



6 8 10 

DAYS POSTEXPOSURE 



12 



14 



Fig. 2 Composite normalized retention on the baeks of cows, comparing 
particle size and cattle kept under pasture conditions and under feedlot 
conditions. Curves 1 and 3 are for 88- to 175-/i sand; curves 2 and 4, for 175- 
to 3 50-ju sand. 



RATE OF PASSAGE OF NEAR-IN FALLOUT IN THE GUT 



The radiation dose to segments of the gut would be from unabsorbed near-in 
fallout reaching the gut by either ingestion or inhalation. The radiation dose to 
the whole gut or to any segment is proportional to the average time that 



176 



JOHNSON AND LOVAAS 



particles spend in any location. The definition of the mean retention time or 
mean transit time is the summation of times that individual particles spend in 
the gastrointestinal tract divided by the total number of particles. By this 
definition, however, mean retention time is very difficult to determine. 

If the ruminant gut is considered in a one-compartment model where mixing 
of digesta is very rapid and emptying is by first-order kinetics, the mean 
retention time can be calculated very simply. It is the reciprocal of the 
first-order rate constant, or 1.44 times the biological half-time. A typical 
excretion curve of 88- to 175-/I sand particles in sheep is given in Fig. 3. 

The true estimate of the mean retention time (?) from such data is the 
weighted average abscissal value (i.e.. the centroid of the curve), and, if the 
function of the curve is not known, mean retention time must be determined by 
approximation methods. From our data, however, the area under the buildup 
portion of the curve is small compared with the total area, and there is little 
error in calculating 7 from the measured half-life. 



00 


= 111 


1 1 ! 1 1 


= 


LU 
CJ 
LU 


_ I V 






LL 








"= 


z 






X\X 


— 


z 
o 
h- 


— 


5 


< X x 

x Ti = 13 hr 





< 


— 




x\ x 2 


— 


z 






x \ 




LU 

u 
z 
o 
u 

LU 






X 

* X X 


— 


> 










h- 


_ 1 




— 


< 


1 






_J 


i 


* N. 




LU 


J 






a: 


r 




— 




: 




x y 




- J 


X 






" 




>v ~* 




x 1 1 1 


I I I I I 


r 



40 



80 120 

TIME, hr 



160 



200 



Fig. 3 Typical excretion function of a single dose of 88- to 175-ju ' Lu- 
labeled sand in sheep. 



RETENTION OF SIMULATED FALLOUT 177 

There is actually a great amount of data in the animal-science literature on 
the rate of passage of digesta in ruminants since this is an important factor in 
determining nutritional efficiency of feedstuffs. 1 Rate of passage as calculated 
from our model is simply the average mass of rumen digesta at any time divided 
by r. 

The values observed from our study are shown in Table 1. They are, in 
general, greater than those reported in the literature for feedstuffs of the same 
particle size. The data in Table 1 show little difference caused by sand particle 
size but an appreciable difference between sheep and cattle. 



Table 1 

MEAN LIFETIMES OF SIMULATED NEAR-IN FALLOUT 
IN THE GUT OF SHEEP AND CATTLE 

Lifetime in Lifetime in 
Sand size, ju sheep, days cattle, days 

88 to 175 1.2 4.8 

175 to 350 1.1 



A very important finding was that for both sizes of sand and with both sheep 
and cattle there was 98 to 100% recovery. This implies that very little, if any, of 
the sand particles are trapped in fine structures of the GI tract. 

Again we must stress that our data correspond to normal intake conditions. 
If dose to the GI tract is sufficient to cause appreciable damage, then decreases 
in motility are to be expected; this would increase retention times and further 
increase the dose. 



REFERENCE 

1. C. C. Balch and R. C. Campling, Rate of Passage of Digesta Through the Ruminant 
Digestive Tract, in Physiology of Digestion in the Ruminant, pp. 108—123, Second 
International Symposium, Ames, Iowa, 1964, R. W. Dougherty et al. (Eds.), Butter- 
worth & Co. (Publishers) Ltd., London, 1965. 



SIMULATED-FALLOUT-RADIATION 
EFFECTS ON SHEEP 



L. B. SASSER, M. C. BELL, and J. L. WEST 

UT— AEC Agricultural Research Laboratory, Oak Ridge, Tenn. 



ABSTRACT 

Sixty-four yearling lambs were exposed to the following radiation treatments: (1) Y beta 
irradiation of the gastrointestinal tract (2.4 mCi/kg of body weight for 3 consecutive days, 
(2) 90 Y beta irradiation of the skin (57,000 rads), (3) 60 Co irradiation of the total body 
(240 R), or (4) all possible combinations of these treatments. Irradiation of the 
gastrointestinal tract produced severe injury to the rumen and abomasum and resulted in 
severe anorexia and diarrhea and a significant loss (>20%) of body weight. Nearly 50% of 
the lambs subjected to combined gastrointestinal and whole-body irradiation died within 60 
days, but lambs in other treatment groups were able to recover from the initial irradiation 
insult. Skin irradiation caused no immediate threat to life but affected survival several 
months postirradiation. Implications of multiple irradiation trauma on animal survival are 
discussed from a postattack recovery viewpoint. 



In the event of a surface thermonuclear detonation, farm livestock located 
downwind from the site of attack would be vulnerable to fallout radiation. The 
response of grazing livestock to fallout radiation would result from the 
combined insults of external whole-body gamma irradiation, irradiation from 
contaminated feed, and beta irradiation to animals' skin. Considerable informa- 
tion is available on the effects of whole-body gamma radiation on large 
animals, ' and incidences of skin irradiation from radioactive fallout have been 
reported in livestock 3 ' 4 as well as in man. 5 Less is known about the response of 
the gastrointestinal tract of large animals to ingested radioactive materials. Nold, 
Hayes, and Comar, 6 measuring internal radiation doses in dogs and goats using 
implanted glass-rod dosimeters, reported that, when a soluble 90 Y solution was 
given, the greatest doses were measured in the lower large intestine. Lethal levels 
of ingested soluble 144 Ce— 144 Pr severely damaged the rumen and omasum of 
sheep. More recently it has been shown that ingestion by sheep of insoluble 
Y-labeled fallout simulant at levels to be expected in fallout contamination 

178 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 179 

severely affected animal health and productivity but was seldom lethal. 8 
Furthermore, the sites of major damage were confined to the rumen and 
abomasum. 

Even though previous studies demonstrate the effects of radiation on 
livestock, few studies have been conducted to determine the interaction of 
simultaneous administration of multiple modes of irradiation. Baxter et al. 9 
reported that the additional trauma of thermal burns increased mortality in 
whole-body X-irradiated (400 R) swine. George, Hackett, and Bustad 10 irra- 
diated lambs by three different methods (whole-body X-ray, oral l 1 I, and beta 
irradiation of the skin) to study the additive effects at two planes of nutrition. 
None of the single or combined treatments were lethal, and weight gain appeared 
to have been influenced mainly by the nutritional treatments. The need for 
information on the survival of large animals in a postattack fallout situation was 
recently emphasized, 1 l and this study was initiated to investigate these 
interactions. 



EXPERIMENTAL PROCEDURES 

Yearling wether lambs of mixed breeding were treated for parasites, shorn, 
and gradually adjusted to a 680-g ration of pelleted alfalfa preconditioned with 
140 g of water. The ration, which was supplemented with trace-mineralized salt, 
represented about 80% of ad libitum consumption. The sheep, averaging 
31.1 ±0.6 kg in weight, were placed in collection stalls approximately 7 days 
before irradiation. One wether was randomly assigned to each of eight treatment 
groups: (1) control, (2) gastrointestinal irradiation (GI), (3) whole-body gamma 
irradiation (WB), (4) skin irradiation (Skin), (5) WB + Skin, (6) Gl + Skin, (7) 
GI + WB, and (8) GI + WB + Skin. Eight replicates of each treatment were made 
over a period of 9 months. 

A sublethal bilateral exposure of 240 R (midline dose of 145 rads) at 
1 R/min from 6 Co sources 12 was used for whole-body gamma irradiation. 
Sheep assigned to the four treatments requiring gamma irradiation were 
simultaneously irradiated 12 to 16 hr before gastrointestinal and skin irradiation 
began. Four 43-by-28-cm, flexible, sealed 90 Sr— 90 Y plaques 1 with surface 
dose rates ranging from 913 to 15 70 rads/hr were used to irradiate about 12% of 
the body area. A plaque was affixed to the thoracolumbar region of the back of 
each sheep and left until a total beta dose of 57,000 rads had been delivered. 
The ratio of skin beta dose to whole-body gamma dose in the combined 
treatments was 240 to 1 — the ratio estimated for the cattle exposed during the 
Trinity shot 3 in 1945. 

The insoluble labeled fallout simulant ( 90 Y-labeled silica sand 88 to 175 ;U in 
size) was mixed with the daily ration and fed for 3 consecutive days, as 
previously described. 8 An initial activity of 2.4 mCi/kg of body weight was fed 
on day 1, but, because of Y decay, only 1.8 and 1.4 mCi/kg remained when 



180 SASSER, BELL, AND WEST 

the ration was fed on days 2 and 3, respectively. The specific activity of the 
various batches of sand ranged from about 5 to 10 mCi/g; thus 6 to 17 g of sand 
were fed daily. 

The half-life, energy, and particle size of the synthetic fallout were selected 
to simulate fallout from a 1-Mt or greater surface nuclear burst at a distance 
sufficient for most livestock to survive the gamma dose. The gastrointestinal 
dosimetry procedure and results are described in detail by Wade et al. 1 4 

Consumption of feed and water and excretion of feces and urine were 
recorded daily. Six to seven weeks after treatment, the animals were removed 
from the collection stalls and fed an alfalfa— grass hay and grain ration ad 
libitum. Body weights were recorded periodically throughout the study. 

Fecal samples were oven dried at 60 C, and bremsstrahlung was counted 
with a well-type gamma scintillation counter set to exclude all pulses less than 
2 MeV. This technique required a shorter decay period before counting than did 
beta counting and eliminated the detection of any 9 Sr contaminate. Standards 
were prepared by adding known quantities of 9 Y-labeled sand to non- 
radioactive fecal material. 

Necropsies were performed on all sheep at death and on surviving sheep 
slaughtered 40 to 64 weeks postirradiation. Selected tissues were preserved in 
10% buffered formalin for microscopic examination (detailed histopathology is 
reported elsewhere 1 5 ). 



RESULTS 

Clinical Observations 

Clinical signs of digestive disturbances were manifest in all sheep ingesting 
the synthetic fallout. Anorexia appeared between the fourth and tenth day after 
irradiation and continued in many of the sheep for several weeks (Fig. 1). There 
were no significant differences in severity of anorexia among the various 
Gl-treatment groups; however, the duration of anorexia was less in sheep 
subjected to both GI and Skin irradiation. A significant interaction (P < 0.05) 
was observed among trials for feed intake, but this difference could not be 
correlated with the specific activity or the amount of sand fed. Feed intakes of 
all non-GI treatments did not differ from those of the control animals. 

From minor to severe diarrhea was observed in the sheep after ingestion of 
Y-contaminated feed. Fecal water began to increase 3 to 4 days after 
initiation of °Y feeding, reached a maximum at the fifth or sixth day, and then 
declined, probably as a result of the anorexia (Fig. 2). Another increase in fecal 
water, occurring between days 11 and 17, was not synchronous among all 
Gl-treatment groups. The severe diarrhea was frequently accompanied by a slight 
mucous discharge and occasionally by a discharge of bright red blood, but 
hemorrhagic diarrhea was not evident. Marked changes in fecal water were not 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 181 



CONTROL 



00 



80 — 



O 60 

cc 
(- 
z: 
o 
o 



40 



20 





i i 


1 .'. ••' 1 .U-a 








- i 




» v 


_ k V; ? 

1; \-Aji 


■m 




fi 1 




k 


, Gl + WB 


t o- 


o , Gl + WB + Skin 




I 1 


1 1 1 



10 



20 30 40 

DAYS AFTER IRRADIATION 



m 



Fig. 1 Effect of gastrointestinal irradiation on feed consumption by sheep as 
a percent of feed consumption by control sheep. Feed intake of sheep 
receiving whole-body (WB) gamma and skin irradiation did not differ from 
that of control sheep. 



observed in sheep of the non-GI-treatment groups during the 3-week period, nor 
was diarrhea a frequent occurrence among the surviving sheep after 3 to 4 weeks. 

A marked increase in both water consumption and urine excretion 
(P < 0.05) was also associated with the severe illness of the Gl-treatment groups 
(Table 1). The WB-treatment group also showed a less pronounced drop in water 
intake and urine excreta. However, no significant change in percentage of body 
water per kilogram of body weight as measured by tritium dilution was observed 
in a study using many of these animals (unpublished data). 

An increase in body temperature was frequently observed in sheep of the 
Gl-treatment groups, but this condition was neither continuous nor consistent. 
Pyrexia, however, usually was observed prior to death. 

The changes in body weight during the 10-week period after irradiation are 
shown in Fig. 3. By the second week all the Gl-treatment groups had lost 
approximately 20% of their initial body weight; this was probably a reflection of 
the severe anorexia and diarrhea. The animals receiving the triple insult 
continued losing weight; in this they differed significantly (P < 0.05) from the 



182 



SASSER, BELL, AND WEST 



70 
60 
50 
40 


_rp 


I I I 
t ^-Gl + WB + Skin y t 

\- WB + Skin ' 
I I I 


I 

i 


A\ - 



70 


! I I 

— \Jx/~ Gl + Skm 


I 




- 


60 








- 


50 
40 


^- Skin 
I I I 


I 


\q-i 


- 









i 






I 








I 




I 














x 


Gl + 


WB 














- 


^ 


*k: 


N- 


~K 


WB 


tit 


± 


H 


-h 


~l~ 


i 


■~-i'' 1 


few 








i 






I 












1 





70 


- 




i 


a gi 


1 








: 




! 




- 


60 


- 
























— 


50 


-&M 


% 


< 


Control 


— *■ 


X 4- 


-i- 


+ 


-h 


-j— 


-W 


rKi 


- 


40 






i 




1 








l 




I 







10 15 

DAYS AFTER IRRADIATION 



20 



25 



Fig. 2 Effect of irradiation on the moisture content of fecal excreta. Diarrhea 
occurred only in Gl-irradiated sheep. 



other Gl-treatment groups by the fifth week. A sharp increase in body weight of 
the Gl, Gl + Skin, and Gl + WB groups occurring between days 24 and 35, 
synchronous with the partial recovery in appetite, was probably a reflection of 
rumen fill. 

Skin and Skin + WB irradiated sheep were unable to maintain their body 
weight on the restricted ration and lost over 10% of their weight by the seventh 
week. The WB-irradiated and control animals nearly maintained initial weight 
during this period of feed restriction. During the recovery period of ad libitum 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 



183 



-1- 




X 


<t 


r>) 




X 




+1 


+1 


+1 


+ 1 


+1 


+1 


+1 


+1 


o 

X 


X 
m 


in 

ON 

o 




nO 




c 

X 




-t- 


C 


-1- 




C 


o 

ri 


c 

in 


X 


+1 


+ 1 


+1 


+1 


+1 


+ 1 


+1 


+1 


■c 


rrj 


Cs] 
«0 


C 
rri 








X 



X X O rh 
m m ^ ffi 

+1 +1 +1 +1 



+ 1 +1 

On 



^ r-n o\ m ^< 



X O t^ O 

N ^O "i ^ , 

+1 +1 +1 +1 

On C~> rs in 

X -h On ,-c 

\C \Q "1 ^ 



+1 +1 +1 +1 

m X no no 

NO O t^ On 

m so no ^ 



m ro 


m 


X 




o 


-c 


-t- 

X 


+1 +1 


+\ 


+1 


+1 


+1 


4-1 


+1 


in c^» 

<N X 


CS 


NO 

o 


C 
X 


O 
C 
X 


c 

c 

X 


m 



m 


c 


f^ 


m 


t> 


~ 






t> 




-t 


(N 


i— i 


X 


NO 


t> 


i— 1 


t-H 


*-i 


NO- 


i—l 


— 


X 


c 


+1 


+1 


+1 


+ 1 


+1 


+1 


+1 


+1 


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ri 


rj 


r^ 


0> 


X 


— 


X 


m 


rn 


m 


o 


— 


c 


c 


'—I 


t^» 


O 


rj 


o 


c 


m 


1-1 



TH rH t-i X 

+ 1 +1 +1 +1 

sO <^ fO rr ' 

O tJ- O x 

(N On O <N 



m r\| -+- O 

-h r^ on t-i 

+1 +1 +! +1 

in <N O O 





-1- 


rr, 


-t- 


m 


-t- 
in 


X 


X 


+1 


+ 1 


+1 


+1 


+1 


+1 


+1 


+ 1 


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<-l 

On 


in 


X 

c 


X 


X 


X 

m 

X 


in 
X 
X 


C 



CA) 



o u a 



184 



SASSER, BELL, AND WEST 



30 



20 - 



10 



5 



10 - 



■20 



-30 



I I 

o o ( Control 


i 




J— 


• • , Skin 


/ . 


_ -O , Gl 


//- 


^w^__ 


// ; 






\ / \ 

— b 

i i 


I 



• • , Skin + WB 

o o , Gl + WB 

o o , Gl + Skin 

_ • • , Gl + Skin + WB 




1*1_L 



8 



10 



10 



WEEKS AFTER IRRADIATION 

Fig. 3 Effects of irradiation on body weight (expressed as a percentage of the 
initial weight) of sheep fed a restricted diet for 7 weeks and then fed ad libitum. 



feeding, all surviving animals gained weight. Survival weight at 40 weeks 
(Table 2) was significantly (P < 0.05) lower than that of control sheep for all 
treatments except WB, and the weight gain of Gl + Skin and Gl + Skin + WB 
groups was significantly less (P < 0.05) than that of all other treatment groups. 



Table 2 
EFFECT OF Gl, WB, AND SKIN IRRADIATION ON SURVIVAL OF SHEEP 





Initial 






Deaths 


Treatment 


weight, kg 


weight, kg 


No. 


Days postirradiation 


Control 


31.3 


55.6 a t 






WB (240 R gamma) 


31.1 


56.5 a 

47.5 b 


1 


61i 


Skir. (57,000 rads beta) 


31.1 


3 


55, i 114, 120 


Gl (2.4 mCi 90 Y/kg) 


32.6 


50.5 b 


3 


25, 102,§ 133 § 


WB + Skin 


33.1 


48. 8 b 


2 


156, 239 


Gl + Skin 


31.4 


36.3° 


2 


134,§ 172§ 


Gl + WB 


30.2 


52.7 b 


4 


5, 17, 19, 68§ 


Gl + WB + Skin 


30.5 


37. 8 C 


4 


20, 30, 47, 61 



* Forty weeks postirradiation. 

tThe values followed by the same letter (a, b, or c) are not different at the 5% level of 
significance. 

^Accidental death not attributable to radiation. 

§ Killed following the development of ruminal and/or abomasal fistulae. 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 



185 



90 



Y Excretion and Dosimetry 



90 



Fecal Y excretion levels (as a percentage of the total dose) increased 
rapidly and reached a peak by the third or fourth day (Fig. 4). After feeding of 
the fallout simulant was discontinued, fecal radioactivity declined with an 
effective half-time of less than 1 day. Ninety-nine percent of the 90 Y had 
decayed or had been excreted by 8 to 10 days after feeding. There were no 
significant differences in excretion among the various Gl-treatment groups. 



• , Gl 

A , Gl + WB 

D , Gl + Skin 

O , Gl + WB + Skin 




5 10 

DAYS AFTER IRRADIATION 

Fig. 4 Fecal excretion of 90 Y-labeled sand (percentage of total dose) fed for 
three consecutive davs. 



Radiophotoluminescent glass-rod dosimeters were used to estimate the 
absorbed dose from the ingested fallout simulant in 13 wethers of a similar 



14 



weight and age. The total dose, measured 7 to 10 days after initiation of 
feeding, was greatest in the fundic region of the abomasum (4.8 to 35 krads), a 
site of severe radiation damage. However, the doses measured in the affected 



186 SASSER, BELL, AND WEST 

areas of the rumen were only 0.5 to 5.3 krads and were not different from doses 
measured in the undamaged pyloric region of the abomasum (1.0 to 10.2 krads). 
This was probably due to the inability of the relatively large dosimeters to 
measure the dose delivered by the sand particles lodged among the papillae, 
rather than to a tissue-sensitivity effect. 

Lethality and Gross Pathology 

The number of deaths occurring in each treatment group and the number of 
days between irradiation and death are presented in Table 2. Early deaths 
occurred only in the Gl-treatment groups, except for an accidental death of a 
Skin-irradiated sheep. Nearly 50% of the sheep receiving the two treatments 
involving a combination of GI and WB irradiation died within 60 days, a death 
rate significantly greater (P<0.01) than the mortality from any of the other 
treatments. 

Of the 24 sheep receiving Skin irradiation either as the only insult or in 
combination with GI or WB irradiation, six died between weeks 16 and 39. Four 
additional sheep were in poor condition at 40 weeks, but the remainder of the 
surviving Skin-irradiated sheep appeared to be healthy. 

Abomasal prolapse through a hernial ring occurred in five sheep of the 
Gl-treatment groups 68 to 172 days after treatment (Fig. 5a). In one sheep a 
small rumen fistula developed about 1 cm cranial to the prepuce 134 days after 
treatment, and a fistuous tract was seen in a sheep that died 60 days after 
irradiation. All these sheep were euthanatized due to their terminal condition. 

The radiation damage to the gastrointestinal tract of the Gl-treatment groups 
was similar to damage previously reported from 90 Y irradiation alone. 8 Major 
gastrointestinal lesions of sheep dying during the early period were usually 
confined to the ventral and lateral regions of the rumen and to the 
fundic— pyloric junction and associated laminae of the abomasum. The ventral 
and lateral regions of the rumen usually contained three to four areas of yellow 
polyplike fibrino-necrosis, which became friable and detached with time, leaving 
a smooth, pale, underlying base. By 40 to 60 days, tan or dark-colored scar 
tissue with a central erosion or necrosis was usually present. The abomasum was 
characteristically inflamed and edematous, with a large area of hemorrhagic 
necrosis at the caudal fundus and cephalic pylorus. The laminae were generally 
inflamed and edematous, and the pylorus was occasionally hyperemic and 
edematous. Only a slight increase in hemorrhage could be attributed to the 
added insult of WB irradiation. In several cases there were fibrino-hemorrhagic 
serosal adhesions of the abomasum and rumen to each other and/or to the 
abdominal wall. A purulent exudate was usually associated with the adhesions. 

Damage to the intestines was limited to mild hyperemia and edema of the 
duodenal mucosa. Although the laminae of the omasum was congested in several 
sheep, necrosis of this organ was seen in only one sheep. Hydropericardium, 
dilatated cardiac ventricles, and heavy and edematous lungs were observed in 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 187 

these sheep at necropsy. Sheep of the Gl-treatment groups surviving 40 to 
52 weeks had residual ruminal and/or abomasal scars when slaughtered, and in 
many cases the scars contained eroded or necrotic centers as shown in Fig. 5b. 

The locations of major damage in the gastrointestinal tract in these sheep 
differ from results predicted from dosimetric studies in dogs and goats 
following an ingested dose of soluble Y and studies 7 in sheep receiving lethal 
levels of soluble 144 Ce— 144 Pr. The passage of sand particles through the rumen 
and abomasum appears to be independent of that of feed or fluids; thus 
sedimentation and concentration of these particles in the ventral portion of 
these organs resulted in significantly greater doses than expected from soluble 
material. In the intestinal tract the passage of sand in a homogeneous mixture 
with the less-fluid ingesta prevented settling of the particles and thus reduced the 
dose to the mucosa of the intestine. 

Beta irradiaton of the skin produced erythema, cessation of wool growth, 
moist reaction of plasma exudate, and a gradual formation of a firm crusted mat 
of the wool during the first 4 to 6 weeks. The wool was easily removed if 
mechanically disturbed, but in most cases epilation was not complete until 10 to 
16 weeks after irradiation (Fig. 6a). Along with epilation was sloughing of the 
epidermal layer leaving exposed a hemorrhagic necrotic dermal tissue. The 
healing and repair process was characterized by epithelialization of the periphery 
(2 to 4 cm) of the wound with the sequential development of an ivory horny or 
leaflike material. The central area of the injury of most sheep was still covered 
with necrotic tissue or a granulating surface when the sheep were slaughtered 
(Fig. 6b). The size of the irradiated area had decreased from 43 by 28 cm to 
approximately 25 by 16 cm. On one sheep retained for extended observation, 6- 
by 3-cm horny keratinizations about 3 cm thick developed by 62 weeks. 

Hydropericardium, dilatated cardiac ventricles, and heavy edematous lungs 
were observed in Skin-irradiated sheep at death. However, milder manifestations 
of these abnormalities were common among Skin-irradiated sheep killed 40 to 
64 weeks after irradiation. 

The exact mode of death and the relation between the respirator}' and 
cardiac involvement and the irradiation treatment of these sheep are not clear. 



DISCUSSION 

These results demonstrate that the additional stress of gastrointestinal 
irradiation injury from contaminated feed may cause not only a great loss of 
animal production but also a greater death rate than anticipated from WB 
irradiation alone. The early deaths were practically all due to WB and GI insults. 
The whole-body, gamma LD 5 of sheep at the dose rate used in the present 
study was approximately 200 rads (midline tissue dose). 1 However, when GI 
irradiation damage was imposed, the LD 5 was reduced to 145 rads. With due 
regard for the limited sample size of this study, this is approximately a 25 to 



188 



SASSER. BELL, AND WEST 




Fig. 5a Mucosal surface of the abomasum of a sheep showing the fistula 
through which the lamina of the abomasum had prolapsed 14 weeks after the 
animal received 90 Y-labeled sand. Note the congested and hemorrhagic 
condition of the prolapsed tissue. 




Fig. 5b Residual scar tissue in the rumen of a sheep 14 weeks after it received 
Y-labeled sand. Similar scar tissue existed in all these animals slaughtered at 
40 to 64 weeks. Note the necrotic center of the scar tissue. 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 189 




^ 




Fig. 6a The irradiated area (43 by 28 cm) of a sheep's back 12 weeks after 
irradiation. Note the area of necrosis and die firm mat of undisturbed wool. 




Fig. 6b The irradiated area (28 by 17 cm) of a sheep's back 40 weeks after 
irradiation. Note the ivory horny or leaflike material at the periphery, the 
nodular necrotic center, and the marked decrease in size of the irradiated area. 



190 SASSER, BELL, AND WEST 

30% reduction in the LD 5 from the whole-body gamma-ray dose. The 
mortality and secondary effects, such as loss of body weight, would certainly be 
critical to the livestock industry and would be of national importance as far as 
the food reserve is concerned in an emergency situation. A substantial radiation 
dose to the gastrointestinal tracts of livestock could result in reduction of meat 
production and reduced or lost milk production without causing death to the 
animal. 

The additional stress of beta irradiation of the skin did not affect survival to 
a great extent for several months postirradiation. The loss in body weight was 
statistically significant (P < 0.05), but this might not have occurred if the ration 
had not been restricted. The large contiguous area of irradiated skin is probably 
an extreme situation, complete healing being virtually impossible. The fallout 
injury to the backs of the Alamogordo cattle was not uniform, and areas with 
minor or no injury 7 probably influenced the healing of more severely affected 
areas. 3 The fact that major injury from skin irradiation was delayed may have 
allowed partial recovery from WB and GI trauma before the additional stress of 
skin irradiation was manifest. Thus skin injury from beta burns probably would 
not contribute significantly to sheep mortaility during the period immediately 
following a nuclear attack. However, this does not preclude possible effects of 
skin irradiation on longevity or other physiological mechanisms which can lead 
eventually to abnormal conditions. 

Several deaths resulting from secondary effects occurred several months after 
irradiation. The development of hernias and fistulae would affect the sheep's 
longevity but not its value for food. However, accumulation in the meat of 
soluble fallout material such as l 37 Cs and 90 Sr would be of concern. Most sheep 
with severely damaged skin could be used for food; few cases of liver abscesses 
or internal infection were apparent in these animals at death. During summer 
months vigilance was required in treating the injured skin to prevent severe 
damage from fly larvae. In winter the loss of heat from the damaged skin would 
be a problem and could affect the ability of these animals to grow or even to 
survive. The type of care necessary to prevent animal losses would be practically 
impossible to provide under range conditions. Nevertheless, in cases of food 
shortages, these survivors could still be sources of food if slaughtered prior to the 
onset of serious illness, 16 even though the meat quality and production per 
animal would probably be reduced. 

Consideration must be given to the probability of animal exposure at the 
levels used in the present study. We can assume that a sheep must graze a pasture 
area of 6.8 m 2 to equal the daily feed intake of the sheep in this study and that 
160 mCi/m 2 of gross fission products would be present at time H + 24 hr in any 
area having had an exposure rate of 100 R/hr at H + 1 hr. 1 7 Thus approximately 
1100 mCi of fission products could be produced by time H + 24 hr on the area 
grazed by one sheep during a 24-hr period. The forage would have to retain only 
7% of the fallout to produce the activity fed in the present study on day 1. 
Recent studies of retention of fallout sand indicate values at this level, but 



SIMULATED-FALLOUT-RADIATION EFFECTS ON SHEEP 191 

varying to some degree depending on the particle size, wind conditions, and 
pasture type and density. Because of decay, the fallout arrival time would 
influence the amount of contamination at a given area, but, with due concern 
for all the variables involved, the activity fed in this study is considered to be a 
realistic level. 

From the estimated exposures of the Alamogordo cattle, 3 a ratio of skin 
beta dose to whole-body gamma dose of 240 to 1 was used to determine the skin 
dose, but recent data indicate a beta-to-gamma ratio on plants of 12 to 1 from 
venting of underground nuclear devices. 1 A beta-to-gamma ratio of 10 to 1 was 
not sufficient to produce the severe effects observed in cattle exposed to beta 
irradiation. 3 This matter is probably not critical for postattack planning 
purposes, since even the high doses and the large areas of involvement in the 
present study did not affect animal survival for several months. 

When predicting the vulnerability of farm livestock to fallout radiation, we 
must consider the effect of multiple radiation assaults on the survival and 
productivity of livestock. Many of our underground missile defense systems are 
located in areas of grazing livestock, and the possibility of surface nuclear 
attacks raises the question of the vulnerability of the livestock to fallout 
radiation. 



ACKNOWLEDGMENTS 

The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U. S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was supported bv funds from the U. S. Office of Civil Defense and 
is published with the permission of the Dean of the University of Tennessee 
Agricultural Experiment Station, Knoxville. 

REFERENCES 

1. D. G. Brown, R. G. Craglc, and T. R. Noonan (Eds.), Proceedings of a Symposium on 
Dose Rate in Mammalian Radiation Biology, Apr. 29— May 1, 1968, Oak Ridge, Tenn., 
USAEC Report CONF-680410, UT-AEC Agricultural Research Laboratory, July 12, 
1968. 

2. D. G. Brown, Clinical Observations on Cattle Exposed to Lethal Doses of Ionizing 
Radiation,./. Amer. Vet. Med. Ass., 140: 1051-1055 (1962). 

3. D. G. Brown, R. A. Reynolds, and D. F. Johnson, Late Effects in Cattle Exposed to 
Radioactive Fallout, Amer. J. Vet. Res., 27: 1509-1514(1966). 

4. C. F. Tessmer, Radioactive Fallout Effects on Skin. 1. Effects of Radioactive Fallout on 
Skin of Alamogordo Cattle, A rch. Pathol., 72: 175-190(1961). 

5. R. A. Conrad, The Effects of Fallout Radiation on the Skin, in The Shorter-Term 
Biological Hazards of a Fallout Field, Dec. 12-14, 1956, Washington, D. C, G. M. 
Dunning and J. A. Hilcken (Eds.), USAEC Report M-6637, pp. 135-141, U. S. Atomic 
Energy Commission and the Department of Defense, 1956. 



192 SASSER, BELL, AND WEST 

6. M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in 
Live Experimental Animals — II, Health Phys., 4: 86-100 (1960). 

7. M. C. Bell, Airborne Radionuclides and Animals, in Agriculture and the Quality of Our 
Environment, N. C. Brady (Ed.), pp. 77-90, Symposium No. 85, American Association 
for the Advancement of Science, Washington, D. C, 1967. 

8. M. C. Bell, L. B. Sasser, J. L. West, and L. Wade, Jr., Effects of Feeding 90 Y-Labeled 
Fallout Simulant to Sheep, Radiat. Res., 43: 71-82 (1970). 

9. H. Baxter, J. A. Drummond, L. G. Stephens-Newsham, and R. G. Randall, Reduction of 
Mortality in Swine from Combined Total-Body Radiation and Thermal Burns by 
Streptomycin, Ann. Surg., 137: 450-455 (1953). 

10. L. A. George, Jr., P. L. Hackett, and L. K. Bustad, Triple Radiation Assault on 
Debilitated Lambs, USAEC Report HW-42540, General Electric Company, April 1955. 

11. M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to 
Fallout Radiation. Final Report, USAEC Report TID-24459, UT-AEC Agricultural 
Research Laboratory, Sept. 7, 1967. 

12. J. S. Cheka, E. M. Robinson, L. Wade, Jr., and W. A. Gramly, The UT-AEC Agricultural 
Research Laboratory Variable Gamma Dose-Rate Facility, Health Phys., 20: 3 37 — 340 
(1970). 

13. M. C. Bell, Flexible Sealed y0 Sr— yu Y Sources for Large Area Skin Irradiation, Int. J. 
Appl. Radiat. Isotop., 21: 42-43 (1970). 

14. L. Wade, Jr., R. F. Hall, L. B. Sasser, and M. C. Bell, Radiation Dose to the 
Gastrointestinal Tract of Sheep Fed an Insoluble Beta-Emitter, Health Phys., 19: 57 — 59 
(1970). 

15. J. L. West, M. C. Bell, and L. B. Sasser, Pathology of Gastrointestinal-Tract 
Beta-Radiation Injury, this volume. 

16. J. H. Rust, Report of the National Academy of Sciences Subcommittee for Assessment 
of Damage to Livestock from Radioactive Fallout, J. Anier. Vet. Med. Ass., 140: 
231-235 (1962). 

17. National Academy of Sciences— National Research Council, Damage to Livestock from 
Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D. C, 
Dec. 20, 1963. 

18. J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout 
by Food Crops and Livestock. Technical Progress Report No. 1, Report AD-695683, 
Colorado State University, May 1969. 

19. W. A. Rhoads, R. B. Piatt, R. A. Harvey, and E. M. Romney, Ecological and 
Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and 
Short-Term Effects on the Vegetation from Close-In Fallout, USAEC Report PNE-956, 
EG&G, Inc.. Aug. 23, 1968. 



SIMULATED-FALLOUT-RADIATION EFFECTS 
ON LIVESTOCK 



M. C. BELL, L. B. SASSER, and J. L. WEST 

UT— AEC Agricultural Research Laboratory, Oak Ridge, Tennessee 



ABSTRACT 

Cattle ingesting Y-labeled fallout simulant at the rate of 2 mCi/kg of body weight were 
more severely affected than those given 5 7,000 rads beta irradiation to 8% of the dorsal 
body surface. Whole-body irradiation of 240 R from Co at 1 R/min affected only blood 
platelets and leukocytes. When these three treatments were combined on eight steers, all 
died within 54 days. Cattle were more sensitive to simulated-fallout radiation than sheep, 
but major damage from ingested radioactivity was in the rumen and abomasum of both 
species. No data were found on combined fallout-simulant effects on simple-stomach 
animals, but effects are predicted to be less than in ruminants. Sheltering cattle in barns 
would be the most effective practical measure to increase animal survival and reduce 
productivity losses in the survivors. Corralling animals to prevent their grazing heavily 
contaminated pastures would be an alternative where barns are not available. About 80% of 
the 112 million U. S. cattle are on pasture. In a 4-hr roundup time, it is estimated that this 
percentage could be reduced to 34% by corralling about 43 million cattle and by placing 
about 31 million in barns. 



In the event of nuclear war, major farm livestock losses from airbursts would be 
caused principally by blast and thermal injury, whereas losses from surface 
bursts would be caused by fallout-radiation injury. Airbursts would be expected 
to be concentrated on urban areas and would not involve a large number of 
livestock, but fallout from surface bursts would probably include areas with 
heavy livestock populations. Grazing livestock would be exposed to gamma 
radiation to the entire animal, beta radiation to the skin, and beta radiation to 
the gastrointestinal tract. Most of the gamma exposure would come from ground 
fallout, but the total exposure would include the gamma component of fallout 
ingested and also from particles retained on the skin. 

Early reports 1 indicated that beta irradiation was of little consequence in 
affecting livestock survival and production, but more-recent data show that, 

193 



194 



BELL, SASSER, AND WEST 



owing to stratification of simulated fallout particles in the gastrointestinal tract, 
beta irradiation can severely affect survival and productivity of sheep.""" The 
early reports, based on dosimeter readings in dogs and goats fed soluble 90 Y, 
have recently been reconfirmed by Ekman. Funkqvist, and Greitz, 4 who fed 
goats soluble ! 5 Sm and La. 

The purpose of this paper is to report the effects of simulated-fallout 
radiation on yearling beef calves and to predict the impact of fallout radiation 
on the livestock industrv. 



EXPERIMENTAL PROCEDURE 

Sixty-four vearling Hereford steers averaging 184 kg were divided into eight 
groups and randomly assigned to the treatments listed in Table 1. Bilateral 

Table 1 

RADIATION-TREATMENT EFFECTS ON WEIGHTS AND 
SURVIVAL OF YEARLING CATTLE 





nt 


Weights, kg 




Deaths 




No. 


Days after 


Treatme 


Initial 


After 5 weeks 


treatment 


Control 




183.4* ±6.9 


198.9 ±6.6 







WB 




183.5 ± 5.9 


193.5 ±6.1 







Skin 




186.4 ±6.5 


193.9 ±6.2 







GI 




184.3 ±4.9 


149.4±6.5 


3 


14. 44. 61 


WB + Skin 




183.6 ± 5.7 


189.1 ±4.2 


1 


168 


GI + Skin 




184.8 ±2.2 


145.1 ±4.4 


4 


25. 53. 67. 83 


GI + WB 




185.5 ±4.9 


141.5 ± 3.5 


5 


14, 17. 19. 40, 

54 


GI + WB + 


Skin 


183.5 ± 5.3 


135.5 ±9.5 


8 


15, 19, 19, 25, 
25, 27, 33, 54 


Starved control 


171.7 ± 7.4 


155.7 ± 5.3 








Mean values ± standard error. 



exposure to whole-body gamma (WB) irradiation of an air dose of 240 R was 
made at a dose rate of 1 R/min with a 60 Co facility. 5 Whole-body exposure was 
made 12 to 20 hr before the initiation of the other treatments. Exposure of 
about 8% of the body surface 6 (Skin) to beta irradiation was accomplished by 
placing two flexible sealed 90 Sr— 90 Y sources 7 over the thoracolumbar region to 
give 5 7,000 rads at the surface of the hair at the rate of 17 to 25 rads/min. 
Gastrointestinal ( GI ) irradiation was accomplished by feeding 2 mCi of 
90 Y-labeled sand per kilogram of body weight using the previously described 
procedure. 2 In addition to these three treatments and all possible combinations 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 195 

of treatments, there was a control group and a group whose feed was restricted 
to that consumed by the GI group. One animal was exposed to each of the 
treatments at a time with eight replications over a period of 1 1 months. During a 
period of adjustment before treatment and for 5 weeks thereafter, the cattle 
were kept in individual stalls for separation and collection of urine and feces. 
During this time they were daily fed 2.7 kg of alfalfa pellets moistened with 
0.8 kg of water. The 90 Y-labeled sand was mixed with the moistened alfalfa for 
each animal for three consecutive days. The Y averaged 9.4 mCi/g of sand (88 
to 175 Id) at the time of feeding. Steers weighing 184 kg were fed 368 mCi of 
90 Y in 39 g of sand on day 1 ; this quantity had decayed to 284 mCi by day 2 
and to 219 mCi by day 3. Control animals were fed the same quantity of 
nonradioactive sand for each of the 3 days. Feed intake, body temperature, and 
signs of radiation injury were recorded daily. 

After 5 weeks of close observation in the collection stalls, the steers were 
grouped together by trial in large pens with shelter, access to limited pasture, 
and free access to grass hay, water, and trace-mineralized salt. In addition, they 
were fed enough 15%-protein grain mixture to provide a growth rate of about 
0.4 kg daily for the control animals. Body weights and general recovery were 
observed periodically for 40 weeks after treatment. 

In addition to these treatment groups, four yearling Hereford steers of 
comparable size and origin were implanted with glass-rod dosimeters into several 
segments of the gastrointestinal tract by a previously described procedure. 9 
After 3 weeks they were fed 2 mCi 90 Y sand for 3 days. They were subjected to 
necropsy 13 days later, and the recovered dosimeters were read. 

Necropsy examinations were performed on all dead animals, and specimens 
of selected tissues were photographed and then preserved in 10% formalin for 
histological examination. 

RESULTS 

Table 1 shows that deaths occurred onlv in treatment groups including GI 
irradiation, with the exception of one steer that died 168 days after WB and 
Skin irradiation. Of the 20 deaths, 17 occurred within 60 days after treatment, 
and only 7 of the 17 occurred within 30 days. From these data it appears more 
reasonable to use LD 50 /6o tnan LD50/30 for grazing cattle exposed to combina- 
tions of fallout exposures. 

Most of the early deaths were associated with combinations of GI and WB 
exposures with the resulting hemorrhagic necrotic involvement. Damage in the 
four major "pockets" of the rumen was more extensive than was observed in 
sheep. The rumen floor contained large fibrinous masses. In addition, sections of 
the ventral reticular honeycombs of most of the cattle were filled with a 
rubbery, yellow, glandular-appearing material. Minor fibrinous necrotic areas 
were seen in the omasum of most of the steers. Major areas of hemorrhagic 
necrosis were surrounded by edematous hyperemic laminae in the abomasum of 



196 



BELL, SASSER, AND WEST 



all cattle fed 90 Y. Adhesions among the rumen, abomasum, and reticulum were 
frequent, and some involved a mass of gelatinous serosal exudate. Gross lesions 
in the large intestine were restricted to minor areas in the cecum and colon of a 
few steers fed Y sand. Several animals showed degenerative changes in the 
heart. Necropsy results are given in more detail in an accompanying paper. 1 

Data summarized in Table 1 also show that the combinations of radiation 
sources were more detrimental than single exposures not only to survival but 
also to body weight of the animals at 5 weeks after exposure. No animals given 
the combined GI + Skin + WB irradiation treatments survived longer than 
54 days. At 35 days the three surviving steers had lost an average of 48 kg, which 
was the greatest loss by any treatment group. Only the "starved" control steers 
and the steers fed 90 Y sand lost weight. Although feed intake by the starved 
controls was restricted to that of the Gl-treated steers, the Gl-treated steers lost 
25% of body weight, while the starved controls lost 9% and the normal controls 
gained 8%. The excess weight loss by the Gl-treated steers was probably due to 
pyrexia and mild-to-severe diarrhea. 

The depression in feed intake by the Gl-treated steers was dramatic, but only 
minor differences were noted among the four groups fed 90 Y sand (these data 
are pooled in Fig. 1). After 9 days, feed intake averaged less than 5% of the 
controls for the remainder of the 28-day period of observation. Comparable data 
on sheep, also shown in Fig. 1, indicate that depression of feed intake occurred 
later and that appreciable recovery was evident by day 28. Feed consumption by 
cattle and sheep receiving WB, Skin, and WB + Skin treatments was not different 
from the untreated control animals for each respective species. 

Since all cattle were group fed after 28 days of individual feeding, no feed 
data are available on the treatment groups after that time. Observations on the 
surviving cattle are incomplete at this writing, bur the 40 weeks of observations 



100 




I 




i I I 


I 


- 


■ 80 








— c, Sheep 







CONTRO 

CD 
O 


— 






. — m , Cattle 




- 


S 40 
20 


— 


\ 

\ 

• 

\ 


\. 


\ O/O 




- 







I 




-* — «— «— ■ f » — !_, _•_._• — 


._• — ._. — •_. — * — • 





10 15 20 

DAYS AFTER IRRADIATION 



25 



30 



Fig. 1 Feed consumption by sheep and cattle fed Y-labeled fallout 
simulant. Feed consumed by WB- and Skin-irradiated animals was the same as 
that consumed by controls. 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 197 

are complete on four of the eight replications. During this period the average 
kilograms of weight gained per surviving animal for each treatment group were: 
control, 118; WB, 131; Skin, 66; GI, 48; Skin + WB, 58; GI + WB, 36; and 
GI + Skin, 22. None of the animals receiving GI + WB + Skin treatment survived 
beyond 54 days (Table 1). These data show that Gl-treated survivors had 
regained much of the weight lost in the first 28 days (Table 1). 

Body temperature was not significantly different among the controls, WB, 
Skin, and WB + Skin treatment groups for the 25-day postexposure period. All 
cattle fed 90 Y-labeled sand showed elevated body temperature, which persisted 
longer in those with combined GI and WB irradiation. The starved control group 
showed a drop in body temperature, indicating a lowered metabolic rate 
(Table 2). 

Except for the larger exposure area, the skin irradiation changes developed 
similarly to those described by George and Bustad. 1 J A moist reaction 
developed during the first 3 weeks, with crusted plasma and epilation in 8 to 
12 weeks, followed by a hemorrhagic necrosis. 

Whole-body gamma irradiation of 240 R at 1 R/min alone did not give the 
characteristic visible signs of radiation sickness. These animals did show the 
depression of white blood cells and platelets. 

All steers fed °Y-labeled sand had mild-to-severe watery diarrhea. The onset 
of diarrhea varied from 6 to 15 days after initiation of the 90 Y feeding. In about 
half of the animals, this was followed by regurgitation of feed and water. Also 
about half of the animals were audibly grinding their teeth constantly. The loss 
of body fluids from diarrhea and vomiting probably contributed to the death of 
many of these animals. 

DISCUSSION 
General 

The results of these investigations on simulated-fallout-radiation effects on 
beef cattle are similar to the data obtained on sheep. 3 Nevertheless, there were 
differences in response between the two species which would prevent the 
exclusive use of sheep as models for beef cattle. Both species are grazing 
ruminants with many similar physiological functions, but they differ in size and 
grazing habits. 

These data clearly demonstrate that cattle exposed to simulated-fallout 
grazing conditions were so severely affected by the combination of treatments 
that there were no survivors at nonlethal levels of WB exposure where no 
physical signs of radiation sickness were seen from WB exposure alone. 

Skin Exposures 

No deaths occurred from Skin exposure alone, but, in combination with 
other treatments, Skin exposure apparently contributed to increased mortality 



BELL, SASSER, AND WEST 



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SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 199 

rates. Although the flexible, sealed sources exposed rectangular areas of 
28 by 43 cm fairly uniformly, these areas resembled the beta-damaged areas on 
the Alamogordo cows. 12 Healing around the edges reduced the severely 
damaged area by the end of 40 weeks of observation. No data are available on 
the dimensions of the original damaged areas of the cattle exposed in 1945, but 
in 1950 hyperkeratosis was evident from the anterior withers to the tail head 
and extended up to about 2 3 cm laterally from the midline of one of these 
cattle. Some areas of extensive hyperkeratotic plaques and horns measured on 
the preserved hide taken from the same cow in 1960 were 13 by 10 cm with an 
elevation of about 2 cm over most of this surface. The skin exposure of the 
Alamogordo cattle was not uniform, but apparently some of these areas could 
have originally been as large and the damage as extensive as those seen on our 
cattle from the exposed rectangular areas of 28 by 43 cm. Some healing and 
tissue repair is already evident in the Skin-irradiated areas on the cattle, but the 
extensive hyperkeratosis has not developed in those exposed in July 1969. A few 
areas of moderate hyperkeratosis and scaling have developed. 

Frequent insecticide spraying was required to reduce the flv problem on the 
skin-damaged areas during warm weather. Since these cattle had free access to 
shelter and shade, exposure to weather extremes was considerably reduced. 
Animals in other areas of the United States could be exposed to greater climatic 
extremes, and many would have much less protection. The loss of the dorsal hair 
coat covering 8% of the body surface would be expected not only to increase 
thermal losses but also to increase nutrient requirements for tissue repair. This is 
evident by the limited data showing that the Control steers gained 52 kg more 
than the Skin-irradiated steers during the 40 weeks of observation. 

Gl Exposure 

Feeding steers 2 mCi of 90 Y sand per kilogram of body weight was more 
detrimental than feeding 2.4 mCi/kg to sheep. This was reflected in greater 
reduction of feed consumption, increased mortality, and increased organ 
damage. The reduction in feed intake was accompanied by a more severe 
diarrhea, vomiting, and grinding of teeth. Fallout-simulant feeding was calcu- 
lated to represent a 9% forage retention with the calculation procedure described 
previously. 1 Since this corresponds closely to the level of 7% calculated for 
sheep, 2 the results were expected to be quite similar. Possibly cattle are more 
sensitive to GI beta irradiation, or perhaps the larger accumulation of 
90 Y-labeled sand in the damaged areas produced a greater exposure. Dosimetry 
data are incomplete, but preliminary data indicate that the rumen exposure was 
greater than that observed in sheep. 9 

The long-term effects of GI exposure in cattle survivors appear to be less 
than in sheep. None of the surviving cattle developed rumen fistulae or abomasal 
hernia and prolapse, but six sheep fed 90 Y sand developed these sequelae. The 
greater thickness of cattle tissue probably reduced the eventual extent of 



200 BELL, SASSER, AND WEST 

injurious effects on tissues adjacent to the primary site of injury, and no 
adhesions were found between affected organs and the abdominal wall. 

These data show that feeding a particulate fallout simulant of size and 
density similar to early fallout produces results quite different from using 
soluble fallout simulants. 4-13 Early fallout particles would be expected to 
collect in pockets in the gastrointestinal tract of ruminants as shown in this and 
similar studies. 

WB Exposure 

No cattle died from exposure to 240 R at 1 R/min unless this treatment was 
used in combination with other radiation exposures. Except for depressed white 
blood cells and blood platelets, none of these steers showed the depressed 
appetite and other symptoms of radiation sickness described by Brown. 1 
Brown established an Ld 50 /3o of 543 R in a study of 70 adult female Hereford 
cattle exposed to 450 to 700 R at 0.9 R/min; about 10% of the cattle exposed 
to 450 R were lost. More-recent unpublished data from the same laboratory 
show a loss of five of 120 Hereford heifers exposed to 300 R at 0.7 R/min and 
no losses from 200 R exposure. None of these deaths occurred during the second 
30 days after exposure, but four of the eight deaths from a combination of 
WB + GI + Skin exposures were observed in the first 30 days and the other four 
during the second 30-day period. 

Animals surviving the WB component of fallout exposure of 240 R alone 
would be expected to produce almost as well as nonirradiated animals. During 
the 40 weeks of observation, the weight gain of the four WB-irradiated cattle 
averaged 131kg, while the controls gained 118 kg. Data on other animals 
indicate life-shortening WB-irradiation effects, but. when aged cattle cease 
producing or production becomes uneconomical, they are normally culled and 
replaced bv voung breeding stock. 

Combined Effects 

Although no cattle died at a WB exposure of 240 R and all died from a 
combination of WB + GI + Skin, there are no data available for cattle on what 
might be expected from a different forage-retention level or from other 
combinations of exposures. It would be prohibitively expensive to obtain data 
on all possible combinations, but the need for more data is clearly indicated, and 
threshold lethality levels should be determined. These data show that combina- 
tions of two or more radiation injuries are lethal to a greater percentage of 
animals and severely affect productivity of survivors. Whole-body exposures 
affect the bone marrow as the most sensitive target system, and beta exposure to 
the skin and gastrointestinal tract affects the local tissue primarily, but abscopal 
effects are also observed on mineral metabolism. 2 Whole-body gamma radiation 
from 60 Co is reduced bv 50% in about 18 cm of unit-densitv tissue, whereas 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 201 

beta penetration from 90 Y is reduced by 50% by a thickness of only 1 mm of 
unit-density tissue. 

IMPLICATIONS 
Livestock Inventories 

Since the 1967 report on livestock and postattack recovery, 1 5 the inventory 
and productivity of the major classes of livestock have increased. Cattle number 
above 112 million and supply over 50 kg of meat and over 150 kg of dairy 
products per person in the United States annually. Production and consumption 
of pork and poultry products have also increased, With the increase in the 
livestock inventories, the estimated market value for cattle alone has now 
increased to over $20 billion. This is indeed a food reserve worth evaluating in 
terms of reliable vulnerability estimates for fallout effects on survival and 
production of these animals. Cattle can produce highly nutritious food when fed 
products not usable for human consumption. However, if 90% of the breeding 
cattle were lost, about 11 years would be required to replenish the inventory of 
breeding animals; 15 this further emphasizes the need to consider vulnerability 
and protective measures. In contrast, the inventory of poultry and swine is small; 
about 1 year is required to replenish a 90% loss of breeding stock. 15 In even 
greater contrast is the radiation resistance and small inventory of seed grains 
required to resume normal production of food crops. These food crops are 
sensitive to fallout radiation only during the growing season, but livestock are 
sensitive at all seasons of the year. 

The importance of livestock production in helping to improve world protein 
supplies has been reemphasized by Director General Boerma of the Food and 
Agriculture Organization of the United Nations in a new "Indicative World 
Plan." In the short run, he recommended that swine and poultry production be 
increased and that in the more distant future ruminant livestock inventories be 
built up to provide more meat and milk. Recommendations were made also to 
simultaneously increase production of cereals and crop products in the 
developing nations. 1 6 

Loss Predictions 

In estimating survival of livestock populations in a nuclear war, most builders 
of damage-assessment models have used gamma radiation as the only criterion. 
Some estimate that, under the same conditions, half the human deaths will result 
from causes other than gamma irradiation. Soft targets, such as major cities, 
would probably get mostly airbursts, which would cause many thermal and blast 
fatalities among the population. Hard targets would be expected to be hit by 
surface bursts, which increase the fallout fatalities. Livestock are widely 
dispersed and would be affected mostly by fallout from surface bursts. 
Nevertheless, some losses would occur around population centers. In 1969 the 



202 BELL, SASSER, AND WEST 

livestock yards in Chicago, 111., handled 1.1 million cattle and 1 million hogs; 
those in Omaha, Nebr., handled 1.5 million cattle and 1.8 million hogs. 17 
Although marketing is being decentralized, many livestock are in transit through 
large population centers in addition to those destined for slaughter. 

The limited data available in this and the preceding paper 3 show definitely 
that, regardless of the conclusions based on dosimeter readings in animals fed 
soluble radioisotopes, grazing livestock losses from fallout radiation would not 
be limited to gamma irradiation alone. The 1970 Swedish paper 4 based on 
dosimeter readings in goats given a solution of 153 Sm and 140 La neglects the 
physical characteristic of fallout particles in combination with the physiological 
functions of the ruminant gastrointestinal tract. Fallout particles from a surface 
nuclear burst deposited downwind on forage in an area where the gamma 
exposure would be above 200 R would be expected to collect in "pockets" in 
the rumen and abomasum owing to the strong muscular movements of the 
different compartments of these organs. This has been demonstrated not only by 
recovery of sand particles but also by observation of damaged areas and by 
dosimetry measurements. Radiation irritation to the colon would be expected to 
reduce the further beta exposure by increasing the rate of passage and by 
reducing water reabsorption in the lower large intestine. The reports from 
dosimeter readings in dogs and goats 4 ' 13 are from levels of soluble isotopes 
which showed minor to no physiological responses. Soluble isotopes would be 
expected to adsorb to feed particles and move in a homogeneous mixture with 
the ingesta. Early fallout levels apt to affect livestock survival would not be 
expected to have a solubility above 10%, but radiations from 153 Sm and l La 
appear to be characteristic of beta and gamma-ray emissions of mixed fission 
products. For animal research the gamma radiation from 153 Sm and La 

would increase the hazard to personnel using these isotopes to label fallout- 
simulant sand particles, but the beta energy would be more characteristic of 
early fallout than that from 90 Y used in most other studies. 

Data available on grazing livestock indicate that cattle are the most sensitive 
species to combinations of fallout exposures. Therefore damage-assessment 
estimates should concentrate on cattle since they supply more food products 
and require more time to replenish breeding stock than any other U. S. food 
source. Since there were no losses of cattle exposed to 240 R of gamma 
radiation but there was 100% loss of those exposed to 240 R of WB + GI + Skin 
irradiation, it is difficult to estimate the LD 50 /6o gamma exposure when 
combined with the beta exposure. Based on the limited data available, very 
rough estimates of LD 50/60 exposures for livestock in barns and corrals or pens 
and for those grazing heavily contaminated pastures are presented in Table 3. 
Data on sheep represent a 7% forage retention of fallout with the combined 
effects being lethal to four of eight animals; 3 data on cattle are for 9% forage 
retention with a loss of eight out of eight exposed animals. Apparently 
differences between these species are greater than can be accounted for by 
forage-retention differences. No data are available on cattle consuming forage at 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 203 



Table 3 

ESTIMATED LIVESTOCK LETHALITY (LD 50/60 ) FROM 

FALLOUT-GAMMA-RADIATION EXPOSURE ALONE AND IN 

COMBINATION WITH BETA RADIATION 



LD50/6O1 total gamma exposure, R 



Barn Pen or corral Pasture* 

(WB) (WB + Skin) (WB + Skin + GI) 

Cattle 500 450 180 

Sheep 400 350 240 

Swine 640 600t 550t 

Equine 670 600t 350t 

Poultry 900 850t 800t 



* Assumed forage retention of 7 to 9%. 
tNo data available. 



the extremes of 5 to 25% forage retention reported by the Colorado workers 
using 88- to 175-/i sand. Also, no data are available on the effects of smaller 
radioactive fallout-simulant particles on the gastrointestinal tract of sheep or 
cattle. 

Estimates in Table 3 on combined effects on swine, equine, and poultry were 
obtained, not from research results, but from estimates based on grazing habits 
and on gastrointestinal anatomical and physiological functions of these species. 

To determine the number of animals which might be exposed, we can make 
assumptions on the different management practices for the classes of livestock 
within each species. A very rough estimate has been made of the normal 
numbers of the 112 million cattle expected to be on pasture, in penned or 
corralled areas, and in shelters (Table 4). The 4-hr roundup time does not imply 
that livestock producers would neglect other emergency procedures to protect 
livestock, but only what might be done in 4 hr to help protect cattle. 

Removal from pasture offers the greatest protection to grazing livestock, as 
shown in Table 3. Pastured dairy cows are normally near the milking parlors and 
would be much easier to confine than other cattle. Milk cows and some calves 
creep-fed on pasture would get supplemental grain, and thus their intake of 
radioactive fallout would be diluted, but almost all other grazing cattle would 
depend entirely on pasture forages and mineral supplements. It would be futile 
to attempt to corral animals in the large range cattle operations in a short time, 
and 4 hr is insufficient time for many range operations. The operators of small 
family farms, which are typical of most of Tennessee farms, would be able to 
confine cattle in a short time. For this reason the surveys by Griffin are more 
optimistic than the data presented in Table 4. His pilot survey covered 176 farms 
in Tennessee, but no data were found for the entire United States. Again it 
should be emphasized that the greatest reduction in the number of lethalities can 



204 



BELL, SASSER, AND WEST 



Table 4 

ESTIMATED NUMBERS OF U. S. CATTLE SHELTERED 

OR CORRALLED INITIALLY AND AFTER A 

4-HR ROUNDUP EFFORT 







Number in 


millions 






Milk 


Feedlot 


Other 






cows 


cattle 


cattle 


Total 


Shelter 










No warning 


3 


< 1 


1 


5 


4-hr roundup 


8 


3 


20 


31 


Pen or corral 










No warning 


4 


10 


4 


18 


4-hr roundup 


5 


8 


30 


43 


Pasture 










No warning 


7 


1 


81 


89 


4-hr roundup 


1 


< 1 


36 


38 


Total 


14 


12 


86 


112 



be made by preventing livestock from grazing for the first few days after fallout 
arrival (Table 3). 



Productivity of Survivors 

WB Effects 

Gamma irradiation alone had no effect on rate of weight gain of cattle 
surviving exposure to 240 R at 1 R/min given as discussed previously, and no 
measurable effect was seen on the sheep exposed to the same treatments, as 
reported by Sasser, Bell, and West. 3 Differences were not statistically significant, 
but WB-irradiated sheep gained 25 kg in 40 weeks, whereas controls gained 
24 kg. These data are in agreement with earlier reports on swine, 2 minor effects 
on milk production, 2 1 ,22 and minor. effects on poultry. 3 

Reproductive performance has not been affected in 179 surviving beef cows 
covering 8 years after an acute WB exposure, and offspring performance has not 
been different from control performance. 24 Embryos of food-producing animals 
exposed to a minimum of 100 R are sensitive to bone deformities for only 
3 days during the first trimester of pregnancy. 



24,25 



WB + Skin Effects 

Livestock surviving in open pens, corrals, and feedlots could receive 
sufficient exposure to affect productivity. The skin exposures of the cattle 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 205 

discussed previously and those of sheep 3 were sufficient to reduce weight gains, 
and the exposure levels were quite similar to those reported for the nonlethal 
exposure of cattle at Alamogordo in 1945. 12 Skin-irradiated sheep gained 16 kg 
in 40 weeks; controls gained 24 kg. Observations are incomplete on cattle, but 
the 40-week gains (in kilograms) on four animals per treatment were: control, 
118; WB, 131; Skin, 66; and Skin + WB, 58. All these animals had access to 
shelter; greater thermal losses would be expected under more-extreme environ- 
mental conditions. Skin irradiation at levels causing alopecia would also be 
expected to reduce milk production and increase problems from external 
parasites, which could also lower productivity and reduce survival. 

WB + Skin + GI Effects 

Livestock ingesting sufficient radioactive fallout to elicit a physiological 
response would almost always be expected to be exposed to WB and Skin 
irradiation levels sufficient to cause physiological changes. The four sheep 
surviving a combination of these three treatments recovered from the early 
weight loss, but the net 40-week gain was only 7 kg compared with 24 kg for the 
eight controls. No cattle survived a combination of these three treatments. 
Observations are continuing on the survivors of GI exposure alone and in 
combination with either Skin or WB. The conclusion is therefore made that 
grazing ruminants surviving in a fallout field where the gamma exposure is above 
100 R would suffer a large reduction in productivity. No data are available on 
simulated exposure of grazing simple-stomach livestock, but effects would 
probably be less than in grazing cattle and sheep. 

Protective Measures 

Ideally, fallout shelters with high protection factors would save the most 
livestock from radioactive fallout in the event of a nuclear war. From a practical 
viewpoint, existing barns providing a protection factor of 2, as shown in the 
limited survey by Griffin, 1 9 would offer protection much greater than that from 
the reduction in gamma exposure alone. Cattle in barns would probably survive a 
gamma contour (measured 1 m above the ground in the open) ten times greater 
than cattle grazing on pasture. 

Cattle restricted to a small area with a high density of animals and limited or 
no grazing opportunity would have a much better chance of survival than those 
on pasture. They would provide mutual shielding against gamma exposure and, 
more important, would not receive the high-level GI exposure. In the USSR it 
was suggested that canvas and blankets may be used to protect the skin of large 
animals. Also suggested was a chemically treated protective muzzle bag to be 
used on cattle to reduce inhaled fallout and to prevent them from eating 
contaminated feed. 

Prevention of grazing of contaminated pastures for the first few days is one 
of the major ways of reducing lethality and productivity losses. Under these 



206 BELL, SASSER, AND WEST 

conditions, giving cattle and sheep no feed at all is much better than permitting 
them to graze heavily contaminated pastures. Farm livestock can survive many 
days without feed but only a few days without water. Providing water for 
animals in barns and/or pens would be an additional problem. 

ACKNOWLEDGMENTS 

The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U. S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was supported by funds from the U.S. Office of Civil Defense and 
is published with the permission of the Dean of the University of Tennessee 
Agricultural Experiment Station, Knoxville. 

REFERENCES 

1. National Academy of Sciences— National Research Council, Damage to Livestock from 
Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D. C, 
Dec. 20, 1963. 

2. M. C. Bell, L. B. Sasser, J. L. West, and L. Wade, Jr., Effects of Feeding 90 Y-Labeled 
Fallout Simulant to Sheep, Radiat. Res., 43: 71-82 (1970). 

3. L. B. Sasser, M. C. Bell, and J. L. West, Simulated-Fallout Radiation Effects on Sheep, 
this volume. 

4. L. Ekman, B. Funkqvist, and U. Greitz, Beta- and Gamma-Dose Measurements in the 
Gastrointestinal Tract of Goats with LiF Dosimeters After a Single Intake of Simulant 
Mixed Fission Products, Report FOA-4-4418, The Research Institute of National 
Defense, Stockholm, Sweden, March 1970. 

5. J. S. Cheka, E. M. Robinson, L. Wade, Jr., and W. A. Gramly, The UT-AEC Agricultural 
Research Laboratory Variable Gamma Dose-Rate Facility, Health Phys., in preparation. 

6. S. Brody, Bioenergetics and Growth, Reinhold Publishing Coorporation, New York, 
1945. 

7. M. C. Bell, Flexible Sealed 9 °Sr- 90 Y Sources for Large Area Skin Irradiation, Int. J. 
Appl. Radiat. Isotop., 21: 42-43 (1970). 

8. C. S. Hobbs, S. L. Hansard, and E. R. Barrick, Simplified Methods and Equipment Used 
in Separation of Urine from Feces Eliminated by Heifers and by Steers, J. Anim. Sci., 9: 
565-579 (1950). 

9. L. Wade, Jr., R. F. Hall, L. B. Sasser, and M. C. Bell, Radiation Dose to the 
Gastrointestinal Tract of Sheep Fed an Insoluble Beta-Emitter, Health Phys., 19: 57-59 
(1970). 

10. J. L. West, M. C. Bell, and L. B. Sasser, Pathology of Gastrointestinal-Tract 
Beta-Radiation Injury, this volume. 

11. L. A. George and L. K. Bustad, Comparative Effects of Beta Irradiation of Swine, Sheep, 
and Rabbit Skin, in Swine in Biomedical Research, Proceedings of a Symposium, 
Richland, Wash., July 19-22, 1965, L. K. Bustad and R. O. McClellan (Eds.), USAEC 
Report CONF-650708, pp. 491-500, Battelle-Northwest. 

12. D. G. Brown, R. A. Reynolds, and D. F. Johnson, Late Effects in Cattle Exposed to 
Radioactive Fallout, A mer. J. Vet. Res., 27: 1509-1514(1966). 

13. M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in 
Live Experimental Animals, Health Phys., 4: 86-100 (1960). 



SIMULATED-FALLOUT-RADIATION EFFECTS ON LIVESTOCK 207 

14. D. G. Brown, Clinical Observations on Cattle Exposed to Lethal Doses of Ionizing 
Radiation, J. Amer. Vet. Med. Ass., 140: 1051-1055 (1962). 

15. M. C. Bell, Livestock and Postattack Recovery, in ^Proceedings of the Symposium on 
Postattack Recovery from Nuclear War, Fort Monroe, Va., Nov. 6—9, 1967, Report 
CONF-671135, pp. 43-58, Office of Civil Defense, Office of Emergency Planning, and 
National Academy of Sciences— National Research Council, April 1968. 

16. A. H. Boerma, A World Agricultural Plan, Set. Amer., 223: 54-69 (1970). 

17. USDA Consumer and Marketing Service, Livestock Market News, 38: 260 (Mar. 17, 
1970). 

18. J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-ln Fallout 
by Food Crops and Livestock. Technical Progress Report No. 1, Report AD-695683, 
Colorado State University, May 1969. 

19. S. A. Griffin, Vulnerability of Livestock to Fallout Radiation, in Annual Progress 
Report, Civil Defense Research Project, March 1968-March 1969, USAEC Report 
ORNL-4413(Pt. 1), pp. 94-96, October 1969. 

20. R. S. Lowrey and M. C. Bell, Whole-Body Irradiation in the Young Pig: Growth, 
Hematology and Metabolism of 45 Ca and 89 Sr, Radiat. Res., 23: 580-593 (1964). 

21. R. G. Cragle, J. K. Miller, E. W. Swanson, and D. G. Brown, Lactation and Radionuclide 
Metabolism Responses of Dairy Cattle to Lethal Doses of Gamma and Neutron 
Radiation, J. Dairy Scu, 48: 942-946 (1965). 

22. E. W. Swanson, R. G. Cragle, and J. K. Miller, Effects of Irradiation upon Lactation, J. 
Dairy Scu, 48: 563-568 (1965). 

23. D. K. Wetherbee, Gamma Irradiation of Birds' Eggs and the Radiosensitivity of Birds, 
Bulletin No. 561, USAEC Report TID-24521, Massachusetts Agricultural Experiment 
Station, October 1966. 

24. UT— AEC Agricultural Research Laboratory, Annual Progress Report, Jan. 1— Dec. 31, 
1968, USAEC Report ORO-672, October 1969. 

25. B. H. Erickson and R. L. Murphree, Limb Development in Prenatally Irradiated Cattle, 
Sheep and Swine, J. Anim. Sci, 23: 1066-1071 (1964). 

26. G. A. Malinin (Ed.), Civil Defense in Rural Regions — A Textbook, Military Publishing 
House of the USSR Ministry of Defense, Moscow, 1965. (STS Order No. 5666 for 
ORNL.) 



PATHOLOGY OF GASTROINTESTINAL-TRACT 
BETA-RADIATION INJURY 



J. L. WEST, M. C. BELL, and L. B. SASSER 

UT— AEC Agricultural Research Laboratory, Oak Ridge, Tennessee 



ABSTRACT 

Fifty-five wether lambs of mixed breeding and seventeen yearling grade Hereford steers fed 
Y-labeled sand as a fallout simulant developed characteristic lesions, particularly in the 
upper digestive tract. These changes occurred in selective areas in the stomach compart- 
ments. Typically there were large, friable, yellowish, elevated areas of fibrino-necrosis in the 
rumen sacs; areas of fibrino-necrosis or hemorrhagic necrosis in the reticulum; small 
hematomas, linear erosions, and focal yellowish necrotic exudate in the omasum; and areas 
of hemorrhagic necrosis in the abomasum. Healing occurred by scar-tissue formation. Scars 
in many instances had tags of necrotic exudate and/or superficial erosions months later. 
Changes in the reticulum and omasum were of appreciably higher incidence and severity in 
the steers than in sheep. Intestinal lesions were also of increased incidence and severity in 
steers as compared to sheep. Exposure of animals to beta skin-plaque irradiation in addition 
to feeding radionuclide did not significantly influence gastrointestinal-tract involvement, but 
whole-body irradiation exerted a definite additive effect. The conclusion that steers are 
more sensitive to the effects of the irradiation procedures employed than are sheep appears 
to be valid. 



Livestock grazing in the area of a surface thermonuclear detonation would incur 
injury and/or death as the result of exposure to external gamma irradiation, 
skin-surface contamination with fallout beta particles, ingestion of fission 
products, or as combinations of these exposures. The extent of injury would 
depend on numerous factors, many of which have been discussed in the light of 
the possibilities of such an occurrence. 1 3 

Nold, Hayes, and Comar, 4 after feeding soluble 9 Y to dogs and goats, 
concluded that the lower large intestine was the critical organ. These 
observations were cited in a subsequent report 1 to serve as models for grazing 
animals. Ekman, Funkqvist, and Greitz 5 found the highest beta concentration in 
the terminal colon of adult goats treated with a mixture of 153 Sm and La. 

208 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 209 

The omasum was the organ severely damaged in the majority of sheep orally 
treated with soluble 144 Ce— 144 Pr; injury to the rumen was found in only one 
animal. No changes were observed in the large intestines at levels that were lethal 
to about 25% of the sheep. 6 Plutonium microspheres in gelatin capsules 
administered to miniature swine by stomach tube produced macroscopic 
necrotic and inflammatory areas in the lymphoid tissue at the ileo— cecal 
junction. Focal microscopic changes were detected throughout the small 
intestine. 7 Clark reported that insoluble 90 Sr administered orally to pigs 
produced areas of damage in the ileum, cecum, and colon but that the principal 
lesions occurred in the stomach (see discussion of Ref. 7). 

The paucity of information regarding the effects in ruminants resulting from 
the ingestion of radioactive fallout products and the necessity of these data for 
arriving at a more realistic evaluation of the results of a nuclear detonation 
prompted this study. 

EXPERIMENTAL PROCEDURE 

The experimental design for these studies has been previously described. 9 l l 
Of the experimental animals, 63 yearling wether lambs of mixed breeding, 
including 8 untreated controls, and 17 treated yearling Hereford steers were 
subjected to necropsy. Procedures involving the preparation and feeding of 
Y-labeled sand were previously reported. 9 Skin of the dorsal thoracolumbar 
region was beta irradiated bv the method described by Bell to expose about 8 
and 12% of the body surfaces of steers and sheep, respectively. An estimated 
5 7,000 rads was delivered to the exposed skin area in a 3-day period. In animals 
subjected to bilateral whole-body irradiation, an exposure of 240 R from 6 Co 
sources was delivered at 1 R/min. The number of sheep examined and the 
treatments were: 38 sheep fed 1.0 to 4.0 mCi of 90 Y-labeled sand per kilogram of 
body weight for 1 to 3 consecutive days; 7 sheep fed 90 Y-labeled sand and 
exposed to skin irradiation; 3 sheep fed 90 Y-labeled sand and exposed to 
whole-body irradiation; and 7 sheep subjected to a combination of the three 
treatments. Steers were similarly treated: 3 steers fed 90 Y-labeled sand at the 
rate of 2.0 mCi per kilogram of body weight for 3 consecutive days; 3 steers fed 
90 Y-labeled sand and exposed to skin irradiation; 4 steers fed 90 Y-labeled sand 
and exposed to whole-body irradiation; and 7 steers subjected to the combined 
treatments. 

Most of the animals were examined in extremis or promptly after death. 
Some animals were destroyed and examined several months posttreatment 
(PT). The day of postmortem examination indicates the time period between 
final treatment and examination; e.g., day 2 indicates that the animal was 
examined 48 hr after the last dose of 90 Y. Representative blocks of tissues were 
fixed in 10% buffered formalin, dehydrated in alcohol, mounted in paraffin, 
sectioned at 6 ju, and routinely stained with hematoxylin and eosin or special 
staining procedures if conditions indicated. 



210 WEST, BELL, AND SASSER 

RESULTS 

General 

In both ovine and bovine species, the most extensive pathologic changes 
occurred in the floor of the caudal half of the ventral ruminal sac (VRS). 
Frequently involvement of the VRS and posterior ventral blind sac (PVBS) was 
continuous. Changes in decreasing severity and extent were present in the 
anterior ventral blind sac (AVBS), the PVBS, and the posterior dorsal blind sac 
(PDBS) of the rumen. Frequently groups of papillae 2 to 5 cm in diameter in the 
vicinity of necrotic lesions were "matted" together or coalesced and were dull 
reddish gray and rather firm. Other individual papillae were enlarged and deep 
red, and the apexes were shrunken and hard. The posterior wall and/or the floor 
of the reticulum was principally affected in cattle but was seldom affected in 
sheep. Omasal alterations were minor and involved the ventral or free aspects of 
the major laminae, usually adjacent to the reticulo— omasal orifice. In the 
abomasum the greater curvature of the caudal fundus and adjacent pylorus were 
the predominant sites of injury. Frequently the involvement extended for 
variable distances anteriorly between two or more fundic spiral folds. The 
mucosa was edematous, hyperemic, and frequently studded with petechial and 
ecchymotic hemorrhages. Spiral folds surrounding ulcers often had sloughed. 
Subserous hemorrhages and gelatinous infiltration occurred frequently, espe- 
cially over mucosal lesions. Fibrinous and fibrous adhesions were commonly 
observed between organs and/or the abdominal floor. The entire thickness of the 
walls of the rumen, reticulum, and abomasum was affected in moderately severe 
and severe lesions. 

Sheep 

The severity of lesions was variable; usually lesions produced were 
proportional to the amount of radionuclide fed. The usual biologic variation, 
however, was observed. ' ] 3 

Oral Treatment 

No lesions were detected in sheep examined at days 0, 1, and 2. An ovoid, 
tan, elevated, necrotic plaque (3 by 4 cm) with several polypoidlike nodules 
around the periphery was observed in the VRS on day 3. Five smaller, soft, 
fluctuating, tan, polypoidlike nodules were in the floor of the PVBS. Similar 
ruminal changes were observed on day 5, and a few small hematomas involved 
two omasal laminae. Similar and somewhat more extensive changes were found 
in all ruminal compartments on day 6. A small tan nodule was observed in the 
reticulum. A few superficial erosions and ecchymotic hemorrhages were seen on 
a few omasal laminae. The abomasal mucosa was hyperemic, with a few lineal 
hemorrhages on the free borders of a few fundic spiral folds. An area of 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 211 

hemorrhagic necrosis (3 by 4 cm) with a fibrinous exudate was observed in the 
caudal fundus. Ruminal changes were similar but more extensive by day 7, but 
the reticulum and omasum were unchanged. A large area of hemorrhagic necrosis 
involved the abomasum. On day 9 more extensive but similar ruminal involve- 
ment and a few yellowish nodules in the reticulum were observed. A few major 
omasal laminae had superficial linear erosions and a few adherent vellowish 
nodules. Abomasal changes were somewhat less severe than on day 7. 

Similar but less extensive ruminal changes were observed on davs 10 and 11. 
The reticulum and omasum were not affected. The abomasal mucosa and 
submucosa were markedly edematous and hyperemic with a small area (1 by 
1.5 cm) of hemorrhagic necrosis. Ruminal changes on day 13 were similar to 
those observed on day 9, and there were no alterations in the reticulum and 
omasum. The abomasal mucosa was slightly hyperemic and edematous. 

A Y-shaped, partially healed scar with scattered necrotic tags was observed in 
the AVBS on day 17. Fibrino-necrotic plaques in the other compartments were 
detaching at the edges or "rolling up", exposing granular hemorrhagic bases. 
Similar changes were seen on day 18, but the surface exposed by the detaching, 
friable, necrotic plaques was pale and smooth. 

Similar ruminal changes were observed on day 21. An elliptical area of 
hemorrhagic necrosis in the abomasum was covered with a mottled, reddish-tan, 
fibrino-necrotic exudate. There was a moderate amount of sanguineous fluid and 
of clear, yellowish fluid in the abdominal and thoracic cavities, respectively. The 
lungs were expanded, heavy, reddish gray in color, and edematous. 

Stellate bluish scars with scattered necrotic tags were seen in ruminal 
compartments on day 5 7. The caudal fundus and cephalic pylorus of the 
abomasum over an area measuring 7 by 10 cm were firmly adherent to the 
abdominal wall bv dense fibrous tissue. An ulcer 4 cm in diameter extended 
almost to the skin. The skin overlying this area was cyanotic and rather firm. 
Sheep examined on days 72, 298, 307, 344, 365, and 372 had stellate, 
grayish-white, ruminal and abomasal scars. Several scars were studded with 
variable-sized superficial erosions. 

The mucosa of the proximal duodenum was frequently congested and 
edematous. Changes in other portions of the intestines were insignificant. 

Severe Complications 

One sheep developed a ruminal fistula on day 132. A thick-walled, fistulous 
tract 3.5 cm in length and 1.5 by 2.5 cm in diameter extended from the anterior 
aspect of the posterior pillar of the VRS to the exterior, emerging about 1.3 cm 
anterior to the prepuce. The pillar was eroded. A deep ulcer surrounded by 
dense fibrous tissue was found in the adjacent PVBS. The rumen in this area was 
firmly adherent to the abdominal wall by fibrous connective tissue. 

A soft, fluctuating, epilated, pendulous enlargement (4 by 6.5 cm) anterior 
and sagittal to the prepuce was observed in a sheep on day 66. The hernial sac 



212 WEST, BELL, AND SASSER 

contained 5.5 by 6 cm of the caudal abomasal fundus. The abomasum was 
firmly attached to the hernial ring and a dirty yellow necrotic exudate covered 
the mucosa of the herniated tissue. A scar (3 cm) extended into the pylorus 
from the diverticulum. Eversion-type abomasal prolapse developed in three 
sheep on days 81, 169, and 201. A similar lesion developed on day 171 in a 
sheep that received combined oral and skin-plaque treatment. Since the caudal 
fundus was firmly adherent to the hernial ring by dense fibrous tissue, the 
cephalic pylorus constituted the major part of the prolapsed tissue. The 
prolapsed tissue was hyperemic, markedly edematous, and studded with 
superficial necrotic foci. 

Oral and Skin -Plaque Treatment 

Combined oral and skin-plaque treatment did not appear to influence 
significantly the extent of stomach changes; however, these animals were 
examined 171, 176, 315, 350, 439, and 447 days PT. It is of interest to note 
that the pericardial fluid was increased in these animals. Myocardial atony and 
dilated, thin-walled ventricles were associated with this finding. 

Oral and Whole-Body Treatment 

Three sheep exposed to combined oral and whole-body irradiation were 
examined 2, 15, and 365 days PT. The exudate of the ruminal lesions of the 
animal examined on day 15 was blood stained. A large area of hemorraghic 
necrosis involved the abomasum (Fig. 1). 

Oral, Whole-Body, and Skin-Plaque Treatment 

Ruminal lesions of a sheep examined on day 19 following combined oral, 
whole-body, and skin-plaque irradiation were not increased in size, but the 
exudate contained a significant admixture of blood (Fig. 2). Three fistulous 
tracts originating from ruminal scars were found in a sheep examined on day 58. 
These tracts were surrounded by dense, reactive, fibrous tissue. Ruminal scars 
with superficial erosions were present in a sheep examined 419 days PT. 

Steers 

Oral Treatment 

Steers fed 90 Y-labeled sand were examined 13, 42, and 59 days PT. The 
pharyngeal mucosa of one steer was moderately congested and edematous 
(day 13). Ruminal changes were grossly similar to those in sheep. These changes 
consisted of elevated, yellowish to yellowish-green, necrotic plaques frequently 
accompanied by polvpoidlike masses of similar composition. Detachment of the 
friable necrotic exudate at the borders exposed a roughened, hemorrhagic 
surface (day 42). The necrotic plaques measured up to 12 by 21 cm and involved 



to i 




213 



■* 



Fig. 1 Abomasum of sheep 41, 15 days after oral and whole-body irradiation. 
A 5.5- by 11-cm area of hemorrhagic necrosis involving the fundic— pyloric 
region. Spiral folds in the necrotic area have sloughed. The mucosa and 
submucosa of the entire organ is hyperemic, edematous, and focally 
hemorrhagic. 




Fig. 2 Rumen and reticulum of sheep 10, 19 days after oral, whole-body, and 
skin-plaque irradiation. Rumen PDBS (left) fibrino-necrotic plaque; PVBS 
(lower left) fibrino-hemorrhagic-necrotic plaque; VRS (below) large fibrino- 
hemorrhagic-necrotic plaque; and AVBS (right) large area of fibrino-necrosis 
with a large hemorrhagic ulcer in the center. Reticulum (right) is normal. 



214 WEST, BELL, AND SASSER 

the entire thickness of the wall. Gelatinous exudation, hemorrhage, and 
fibrinous or fibrous adhesions to adjacent organs (or less frequently to the 
abdominal wall) were seen. A tortuous, thick-walled, fistulous tract extended 
from the postero-medial floor of the VRS to the medial wall of the abomasum 
(day 59). Variable-sized scars partially, covered with necrotic exudate were seen 
in the ruminal compartments. An area of necrosis (5 by 7 cm) was observed in 
the reticulum (day 13). A scar (1.5 by 17 cm) studded with small superficial 
erosions was observed on day 42. Omasal changes were limited to focal 
congestion of a few major laminae. An area of hemorrhagic necrosis (5 by 8 cm) 
involved the cephalic pylorus of the abomasum of one steer. The necrotic 
process had extended into the submucosa of the contiguous fundus (day 13). A 
tear-shaped scar (5 by 21 cm) with scattered necrotic tags was observed 
(day 42). The communicating fistulous tract (day 59) from the rumen entered 
the medial aspect of the terminal abomasal fundus. The spiral folds surrounding 
the tract had sloughed. A healed scar (3 by 7 cm) was seen in the caudal fundus. 
The surrounding mucosa was edematous and dirty brownish red in color. 

Scattered areas of congestion were observed in the mucosa of the small 
intestine. A thickened area consisting of numerous nodules up to 1.5 cm in 
diameter was observed at the ceco— colic junction. The centers of some of the 
nodules contained yellow, necrotic plugs (day 42). The ileal and colic mucosae 
(and possiblv the submucosa) of one steer were dull grayish red in color and 
appreciably thickened by transverse ridges (day 59). 

An estimated 16 liters of sanguineous ascitic fluid containing yellowish 
fibrinous aggregates was seen in the steer examined on day 13. Fibrinous tags 
were adherent to the parietal and visceral peritoneum. Three liters of clear ascitic 
fluid was present in the steer examined on day 42. 

Oral and Skin-Plaque Treatment 

Ruminal changes were comparable to those in the previous group (days 20 
and 51). Superficial erosions studded the scars of the animal examined on day 
300. Depressed stellate scars (2 by 8 cm and 1.5 by 16 cm) were observed in the 
reticulum (days 20, 51, and 300). Linear erosions and small yellowish nodules of 
necrotic exudate were observed on some major omasal laminae (day 20). 
Variable-sized scars (12 to 21 by 2 to 4 cm) were observed in the wall of the 
greater curvature of the abomasum (days 20 and 51). The scars extended for 
several centimeters between five laminae (day 20). The surfaces of the scars were 
partially covered with yellowish-green necrotic exudate. There was a stellate scar 
(2 by 12 cm) in the caudal fundus and a second scar (1 by 11 cm) in the cephalic 
pylorus of the abomasum of the steer examined on day 300. Intestinal changes 
were comparable to those in the previous group. 

Oral and Whole-Body Treatment 

Elevated, linear and ovoid, dull gray, superficial erosions studded the mucosa 
of the thoracic portion of the esophagus of steers examined on days 17 and 37. 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 215 

Ruminal involvement was of increased extent and severity, some plaques 
measuring 2.5 by 25 by 30 cm. In addition to the thick, yellowish or 
yellowish-green, friable plaques with polypoid masses (Fig. 3), there were 
elevated, yellowish areas covered with enlarged, sparse papillae. Some necrotic 
plaques (up to 5 by 12 by 14 cm) had completely detached and exposed a 
hemorrhagic granular surface. Necrosis of the reticulum was increased in extent 
and severity and consisted of large yellow or yellowish-green plaques and areas 
of hemorrhagic necrosis with sparse necrotic exudate (Fig. 3). Small linear 
erosions and focal, yellowish, necrotic plaques were observed on a few major 
omasal laminae in three steers. Abomasal changes were comparable to those in 
the previous group, the alterations consisting of large areas of hemorrhagic 
necrosis (Fig. 4) partially covered with yellowish, necrotic exudate (days 12, 15, 
and 17). The fundic spiral folds were moderately to markedly edematous with 
scattered ecchymotic hemorrhages. Deep erosions or ulcers occurred between 
several spiral folds. A scar with a hemorrhagic base was partially covered with 
cream-colored, necrotic exudate (day 37). The overlying serosa was congested, 
roughened, and covered with fibrino-hemorrhagic tags. 

The duodenal mucosa was congested and edematous with small irregular and 
linear hemorrhages. Several gray and hemorrhagic nodules 4 to 5 mm in diameter 
had developed in the mucosae of the lower jejunum, ileum, and the midportion 
of the cecum (day 37). 

Oral, Whole-Body, and Skin-Plaque Treatment 

Superficial, grayish-red, linear streaks were observed in the esophageal 
mucosa (day 12). Changes in the rumen and reticulum were comparable to those 
in the preceding group. Omasal changes were similar but more extensive, 
consisting of linear erosions and hemorrhagic necrosis with necrotic exudate. 
The cavity of the omasum of one steer (day 17) was completely filled with a 
currant-jelly type of blood clot. There were areas of hemorrhagic necrosis (up to 
8 by 28 cm) in the abomasum. The fundic spiral folds were edematous and 
hyperemic with scattered petechial and ecchymotic hemorrhages. A bluish, 
depressed, stellate scar (3 by 13 cm) was present in the abomasum of the steer 
surviving for 52 days. 

The mucosa of the small intestine was congested, and in some there were 
ecchymotic hemorrhages in the wall (days 12, 16, 17, and 18). In one (day 17) 
several areas of hemorrhage (2 to 7 cm) in the wall with fibrino-hemorrhagic 
organizations attached to the mucosa were seen. There were fluid blood and 
blood clots in the lumina. In one steer an ulcer had developed in the mucosa 
over a large area of subserous hemorrhage (day 18). Cecal changes included 
scattered ecchymotic hemorrhages in the wall (day 17), solitary ulcers (days 18 
and 31), a large ulcer over an area of submucosal hemorrhage (day 18), and an 
area (4 by 7 cm) with several small ulcers (day 31). The lumina of both the 
cecum and colon contained fluid blood and blood clots or bloody ingesta. The 



216 



WEST, BELL, AND SASSER 




Fig. 3 Rumen and reticulum of steer 185, 17 days after oral and whole-body 
irradiation. Reticulum (left) with large area of hemorrhagic necrosis. Ruminal 
compartments (left to right), AVBS, VRS, PVBS, have necrotic plaques with 
variable-sized polypoidlike masses of exudate. 




Fig. 4 Abomasum of steer 185, 17 days after oral and whole-body irradia- 
tion. A 7- by 19-cm area of hemorrhagic necrosis involving the fundic— pyloric 
region. Spiral folds in the area are necrotic and have sloughed. The mucosa and 
submucosa are hyperemic, edematous, and focally hemorrhagic. 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 217 

mucosa was congested and studded with petechial and ecchymotic hemorrhages 
with similar hemorrhages being deeper in the wall. 

Microscopic Observations 

Preliminary microscopic observations are based on the examination of tissues 
from 12 sheep exposed to oral treatment only. 

Days 1 and 2 

Foci of "ballooning" or enlarged, rounded, pale staining cells were observed 
in the mucosae of the rumen and omasal laminae. There were a few foci of 
superficial necrosis of the abomasal mucosa. 

Day 3 

Small and larger microcysts formed by rupture of variable numbers of 
epithelial cells were seen in the ruminal mucosa. Although some cysts involved 
only the upper layers of cells, in larger cavities the entire epithelial thickness was 
affected. The cysts contained granular eosinophilic material and cellular debris. 
The eosinophilic material in many cysts was vacuolated. Larger cysts were 
covered by the parakeratotic layer only, but the upper border of some smaller 
cysts was composed of epithelial cells in addition to the parakeratotic layer. The 
cysts were primarily seen in the apical two-thirds of the affected papillae. The 
underlying propria was edematous and infiltrated with polymorphonuclear 
leucocytes (PMN cells). There were numerous areas consisting of groups of 
enlarged papillae. The lamina propria was edematous and contained strands of 
fibrin, and the submucosa was moderately edematous. Foci of necrosis, PMN-cell 
infiltration, and edema were seen in the abomasal mucosa. A slight fibrino- 
cellular exudate covered the necrotic surface. 

Day 5 

Focal sloughing of groups of necrotic luminal papillae exposed the 
submucosa in some areas. Groups of several papillae were distended with plasma 
and fibrin; this situation created a honeycomb effect within the propria. There 
were large areas of fibrino-necrosis of the mucosa (Fig. 5). Hemorrhage and large 
numbers of PMN cells, many degenerating, occurred in the necrotic mass. The 
upper submucosa was moderately edematous and extensively infiltrated with 
PMN cells. The blood vessels were dilated, and the walls of some vessels were 
necrotic. The vascular endothelium was swollen, vacuolated, or hyperchromatic. 
In some vessels the endothelial cells were not evident. The deeper submucosa 
and circular muscle layer were slightly to moderately edematous and infiltrated 
with inflammatory cells. 

There were foci of necrosis and sloughing of the omasal mucosa. The 
submucosa was moderately edematous and infiltrated with PMN cells. There 
were foci of hemorrhage. Large areas of hemorrhagic necrosis involved the 
abomasal mucosa. In some areas a thin layer of necrotic epithelium covered a 
thick layer of hemorrhage which appeared to rest on a thin rim of necrotic 



218 



WEST, BELL, AND SASSER 




Fig. 5 Rumen of sheep 191, 5 days after oral treatment. Right to left, 
marked subserous edema. The mucosa is necrotic and covered with a thick 
fibrinous organization. Remnants of necrotic mucosa on the surface and two 
necrotic laminae propria (left lower center). 



mucosa and the muscularis mucosae. It appeared that rapid and forceful 
hemorrhage had "lifted" the necrotic mucosa into the lumen. Blood vessels at 
the base of the mucosa and adjacent glands were dilated. Some of the vessels 
were characterized by necrotic walls and some by thrombosis. The muscularis 
mucosae was focally interrupted. The submucosa was markedly thickened by 
edema and hemorrhage and was extensively infiltrated with PMN cells. Some 
blood vessels in the upper submucosa had necrotic walls, and some of these 
vessels contained thrombi. The inner muscle layer bundles were separated by 
edema. 



Day 9 

There were large areas of fibrino-necrosis of the ruminal mucosa. Groups of 
papillae were distended with plasma containing fibrin. The submucosa beneath 
the large, necrotic, mucosal areas had necrosis and edema and only a few 
inflammatory cells. Numerous blood vessels in this area were necrotic and 
thrombotic. In other areas the submucosa was edematous, focally hemorrhagic, 
and extensively infiltrated with PMN cells. Focal necrosis of the inner muscle 
layer occurred beneath the more severely affected mucosa and submucosa. 

Foci of superficial necrosis and large areas of hemorrhagic necrosis involved 
the abomasal mucosa (Fig. 6). A large fibrino-hemorrhagic organization was 




219 



w 



■ •. 



Fig. 6 Abomasum of sheep 175, 9 days after oral treatment. Right to left, 
extensive submucosal edema and focal hemorrhage. Necrosis and interruption 
of the muscularis mucosa. Hemorrhagic necrosis of the mucosa with dilated, 
necrotic, and thrombosed vessels at the base of the mucosa. The surface of the 
hemorrhagic-necrotic exudate is covered with a thin layer of necrotic mucosa. 



attached to the surface in one area. Other changes were similar to those found 
on day 5. 

Day 11 

Large areas of fibrino-necrosis of the ruminal mucosa were covered at some 
sites by necrotic epithelium and the parakeratotic layer. The latter was quite 
well preserved. Epithelial cells bordering the necrotic areas were enlarged and 
rounded and the nuclei were pyknotic. Some rete pegs were irregular in shape 
and of increased length. The underlying propria was edematous and extensively 
infiltrated with PMN cells. The submucosa was moderately edematous and 
focally hemorrhagic. There was a moderate infiltration of PMN cells with fewer 
lymphocytes and mononuclear cells. Collagen fibers in the upper submucosa 
were anuclear, swollen, and dull red, and some fibers were "frayed." The walls 
of some blood vessels were necrotic, and some vessels were thrombotic. The 
abomasal changes were comparable to those observed on day 9. 

Days 13 and 18 

The changes were similar to those found on day 11. 



Day 59 

The lining of large areas of the rumen consisted of a mixture of vascular 
granulation tissue and fibroblasts. The fibroblasts were oriented parallel to a 



220 WEST, BELL, AND SASSER 

surface that was "ragged" and superficially necrotic. The underlying collagen 
fibers were swollen. In other areas a layer of dark epithelium with a thickness of 
two to three cells formed the inner lining. The undulant surface had no papillae. 
Rete pegs were absent, sparse and short, or sparse, long, and irregular. The 
edematous submucosa was extensively infiltrated with macrophages. Several 
blood vessel walls were eccentrically thickened. 

Changes in the abomasal mucosa included dilated glands, glandular atrophy, 
atrophy and glandular degeneration with moderate mononuclear infiltration and 
slight infiltration of lymphocytes and PMN cells, focal superficial necrosis, 
necrosis of the entire mucosa, and ulcer formation. A few colonies of large 
bacterial rods were seen beneath the necrotic mucosa. A large area of the 
submucosa forming the base of the ulcer was replaced by vascular granulation 
tissue and fibroblasts. This tissue was moderately infiltrated with macrophages 
and PMN cells. Coagulation necrosis involved another large area of the 
submucosa beneath the ulcer. Several dilated, necrotic, and thrombosed vessels 
were seen in this area. A band of caseous necrosis involved the lower submucosa 
and a portion of the thin muscle layer. The atrophic muscle layer rested on a 
thick layer of collagenous fibers and contained islands of granulation tissue and 
fat. Skin was not present on the sections. 



DISCUSSION 

Regressive cellular changes and cellular necrosis produced by irradiation are 
not pathognomonic. 13 15 Similar changes have been produced by a variety of 
causes. The exact mechanism or mechanisms by which cellular changes are 
produced by irradiation are not known but are probably multiple. 1 3 ! 5 

The pharyngeal mucosa and submucosa were congested and edematous, and 
the esophageal mucosa of a few steers had linear and ovoid erosions. It is 
probable that these changes occurred during regurgitation of ruminal fluids 
rather than as a consequence of ingestion of feed containing the radionuclide. 

Yttrium-90-labeled sand ingested by sheep and cattle collects in rather 
specific ruminal and abomasal sites and produces characteristic pathologic 
lesions. Sand particles lodge between ruminal papillae in these areas and appear 
to be indefinitely retained by the ensuing inflammatory and necrotic exudate. 
Ruminal contractions and compartmentalization by the pillars probably are 
important in determining the areas where radioactivity will be concentrated. In a 
few early lesions, focal accumulation of plasma beneath and within the mucosa 
resulted in dome-shaped, yellowish elevations sparsely covered with enlarged 
papillae. Later, necrosis of the mucosa, increased vascular damage, extensive 
effusion of plasma, and extensive inflammatory cell infiltration produced the 
characteristic large fibrino-necrotic plaques or masses observed in sheep. 
Probably the grossly similar lesions seen in cattle would be comparable 
microscopically. Detachment of the necrotic masses at the borders exposed a 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 221 

hemorrhagic, granular base or a smooth, pale surface, the appearance depending 
upon the age of the lesion. A pale, depressed, stellate scar was apparent on 
detachment of the exudate. Several months after treatment necrotic tags and 
superficial erosions were seen on the surfaces of numerous scars. 

The reticulum was mildly affected in a few sheep. In contrast, necrotic 
plaques or areas of hemorrhagic necrosis were seen in the reticulum of a 
significant number of steers. We have no explanation for this species difference. 

In general, minor lesions only were seen in the omasum of a few sheep. In 
steers the changes were of appreciably greater incidence and severity. The 
omasum of one steer was filled with a currant-jelly blood clot. An area of 
hemorrhagic necrosis between two laminae had apparently eroded into a large 
blood vessel. 

Characteristically injury occurred at the fundic— pyloric region on the greater 
curvature of the abomasum. This selective location is probably due to 
gravitational forces, the sand particles settling in the lowest area of the organ. 
Several variable-sized extensive areas of hemorrhagic necrosis developed in this 
area. Some lesions were covered in part with a thick fibrino-necrotic exudate. 

Anorexia (in the absence of more-severe complications) following treatment 
for variable periods resulted in appreciable weight loss. Ruminal fistula, 
abomasal hernia, and eversion-type abomasal prolapse occurred in six sheep. 
Another sheep probably would have developed an abomasal fistula if it had 
survived. Fibrinous and fibrous adhesions of organ to organ and/or to the 
abdominal floor occurred frequently in sheep. Similar adhesions between organs 
were frequently seen in steers. Only two steers developed ruminal adhesions to 
the abdominal floor. In one steer a long, tortuous, communicating fistulous tract 
extended from the rumen to the abomasum. The cause of this development is 
obscure. Fibrous adhesions of organ to organ or to the abdominal floor would 
interfere with normal function and conceivably could result in strangulation. 
Transportation and other stress-producing experiences may cause separation of 
adhesions and subsequent peritonitis. 

The absence of significant intestinal lesions in sheep was unexpected. 
Intestinal lesions found only in orally treated steers were not severe. The ileal, 
cecal, and colic mucosae (and possibly submucosae) of the intestine of one steer 
were appreciably thickened by transverse ridges. This change was not believed to 
be associated with irradiation, but microscopic examination has not been 
completed. 

Whole-body irradiation superimposed on oral treatment appeared to increase 
the extent and severity of gastrointestinal changes. 

Focal microcyst formation and foci of epithelial necrosis were early ruminal 
mucosal changes. Microcysts were probably the result of cellular imbibition of 
fluid and subsequent rupture of the cells. The cysts were frequently multiple on 
papillae and involved the apical portions of the affected papillae. The underlying 
lamina propria was edematous and infiltrated with numerous PMN cells. 
Microcysts, which are not an unusual ruminal mucosal change in sheep, 



222 WEST, BELL, AND SASSER 

apparently occur as a result of altered physiology. 8 These cysts are not 
associated with inflammation of the lamina propria. Focal effusions of plasma 
into the mucosa caused marked swelling of groups of papillae. The epithelium of 
these papillae was degenerative or focally necrotic. The propria was distended 
with proteinaceous fluid and fibrin; this distention created a honeycomblike 
effect. 

In more advanced lesions large areas of fibrino-necrosis involved the mucosa. 
This exudate consisted of necrotic mucosa, fibrin, and extensive PMN-cell 
infiltration. In some areas the exudate had sloughed and exposed a congested, 
ragged submucosa. The submucosa was edematous, focally hemorrhagic, and 
extensively infiltrated with PMN cells. The blood vessels were dilated. Many 
were necrotic and several thrombosed. The necrotizing reaction extended to the 
serosa in more severely affected areas. The inner surface of a ruminal scar was 
formed by granulation tissue and fibroblasts or a thin (2- to 3-cell thickness) 
layer of hyperchromatic epithelium with no or with scattered, short rete pegs. 
The submucosa was edematous and extensively infiltrated with macrophages. 

Minor changes of focal necrosis of the omasal mucosa with edema and 
cellular infiltration of the submucosa were seen. 

Hemorrhagic necrosis was the characteristic change seen in the abomasal 
mucosa. The submucosa was markedly edematous and focally hemorrhagic. 
Many blood vessels were necrotic and thrombosed. In one animal a chronic ulcer 
had developed. The underlying submucosa was replaced in one area by vascular 
granulation tissue and fibroblasts, which were infiltrated with PMN and 
mononuclear cells. A large area of coagulation necrosis involved an adjacent area 
of the submucosa beneath the ulcer, indicating concomitant repair and 
continuation of an acute reaction. 

Intestinal changes in sheep were minimal. Comparable treatment of cattle 
induced significant lesions. Bacterial invasion of tissue was observed in only a 
few animals. The conclusion that sheep are less sensitive to the radiation 
procedures employed than are cattle appears to be justified. 

ACKNOWLEDGMENTS 

The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U. S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was supported by funds from the U. S. Office of Civil Defense and 
is published with the permission of the Dean of the University of Tennessee 
Agricultural Experiment Station, Knoxville. 

REFERENCES 

1. National Academy of Sciences— National Research Council, Damage to Livestock from 
Radioactive Fallout in Event of Nuclear War, Publication 1078, Washington, D. C, 
Dec. 20, 1963. 



PATHOLOGY OF GASTROINTESTINAL-TRACT INJURY 223 

2. J. H. Rust, Report of the National Academy of Sciences Subcommittee for the 
Assessment of Damage to Livestock from Radioactive Fallout, J. Amer. Vet. Med. Ass., 
140: 231-235 (1962). 

3. H. A. Smith and T. C. Jones, Veterinary Pathology, pp. 658-673, Lea & Febiger, 
Philadelphia, 1966. 

4. M. M. Nold, R. L. Hayes, and C. L. Comar, Internal Radiation Dose Measurements in 
Live Animals, Health Phys., 4: 86-100 (1960). 

5. L. Ekman, B. Funkqvist, and U. Greitz, Beta- and Gamma-Dose Measurements in the 
Gastrointestinal Tract of Goats with LiF Dosimeters After a Single Intake of Simulant 
Mixed Fission Products, Report FAO-4-4418, The Research Institute of National 
Defense, Stockholm, Sweden, March 1970. 

6. M. C. Bell, Airborne Radionuclides and Animals, in Agriculture and the Quality of Our 
Environment, N. C. Brady (Ed.), pp. 77-90, Symposium No. 85, American Association 
for the Advancement of Science, Washington, D. C., 1967. 

7. V. H. Smith, H. A. Ragan, B. J. McClanahan, J. L. Beamer, and J. L. Palotay, The 
Passage Time of Plutonium Oxide in Pigs, in Gastrointestinal Radiation Injury, M. F. 
Sullivan (Ed.), Report of a Symposium held at Richland, Wash., Sept. 25 — 28, 1966, 
Report CONF-660917, pp. 518-523, Exerpta Medica Foundation, New York, 1968. 

8. Alfred Trautmann and Josef Fiebiger, Fundamentals of the Histology of Domestic 
Animals, pp. 182—183, Translated and revised from the eighth and ninth German 
editions, 1949, by Robert E. Habel and Ernst Biberstein, Comstock Publishing 
Associates, Ithaca, N. Y., 1952. 

9. M. C. Bell, L. B. Sasser, J. L. West, and L. Wade, Jr., Effects of Feeding 90 Y-Labeled 
Fallout Simulant to Sheep, Radiat. Res., 43: 71-82 (1970). 

10. L. B. Sasser, M. C. Bell, and J. L. West, Simulated-Fallout-Radiation Effects on Sheep, 
this volume. 

11. M. C. Bell, L. B. Sasser, and J. L. West, Simulated-Fallout-Radiation Effects on 

Livestock, this volume. 

9 9 

12. M. C. Bell, Flexible Sealed Sr— Y Sources for Large Area Skin Irradiation, Int. J. 

Appl. Radiat. Isotop., 21: 42-43 (1970). 

13. W. A. D. Anderson, Pathology, Vol. I., pp. 166-188, The C. V. Mosby Company, St. 
Louis, Mo., 1966. 

14. A. R. Moritz and F. W. Henriques, Jr., Effects of Beta Rays on the Skin as a Function of 
the Energy, Intensity, and Duration of Radiation. II. Animal Experiments, Lab. Invest., 
1: 167-185, 1952. 

15. Philip Rubin and G. W. Casarett, Clinical Radiation Pathology, Vol. I, pp. 1-37, W. B. 
Saunders Company, Philadelphia, 1968. 

16. K. Nieberle and P. Cohrs, Textbook of the Special Pathological Anatomy of Domestic 
Animals, revised by Paul Cohrs, translated by R. Crawford, pp. 364-369, Pergamon 
Press, Inc., London, 1967. 



RESPONSES OF LARGE ANIMALS 
TO RADIATION INJURY 



DAVID C. L. JONES 

Stanford Research Institute, Menlo Park, California 



ABSTRACT 

Recent data pertaining to the relations between dose rate and lethality in sheep exposed to 
dose rates ranging from high (hundreds of roentgens per hour) to low (less than 1 R/hr) are 
incorporated in a review of the field. It is concluded that even within the high dose-rate 
range there is a significant inverse relation between LD50/6O an ^ dose rate and that 
discernible radiation injury does accrue even at dose rates less than 1 R/hr. The chronology 
of lethality and hematologic changes in sheep during continuous exposure to death at dose 
rates of 3.74 and 1.96 R/hr are compared with those observed during terminated exposure 
at 0.84 R/hr. At 1.96 R/hr there is no indication of reduction in survival time by 
overirradiation, whereas at 3.97 R/hr there is a marked compression in the range of survival 
times. Chronology and extent of changes in circulating leukocyte counts vary appreciably 
with dose rate during protracted exposure. 



In April 1968, at the symposium on dose rate in mammalian radiation biology, 
Dr. Norbert Page gave an overview of the effects of dose protraction on radiation 
lethality in large animals. His summary, together with some other papers 
presented at that symposium, furnished an excellent statement of the state of 
the art at that time. In his summary of the entire symposium, Edward Alpen 
pointed up the importance of describing the effects of variation in dose rate in 
considering recovery processes and the untenability of the view that a single 
unique recovery "constant" exists, even for a given species. 

My objective is to update the information presented at the 1968 symposium, 
with particular reference to the sheep. This species is of major interest to this 
present symposium because the sheep is an economically important domestic 
animal resource and because it is the large animal that has been most 
systematically studied with respect to the relations between dose rate and 
response to radiation. 

224 



RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 225 

The information presented comes principally from the most recent technical 
reports of the Naval Radiological Defense Laboratory (NRDL) program in large 
animal radiobiology, published during the last months of that laboratory's 
existence, and from the initial studies under the Office of Civil Defense (OCD) 
program now located at the Stanford Research Institute (SRI). 

Two specific areas are considered: (l)the relation between dose rate and the 
LD50/60 as measured in the terminated type of exposure to a predetermined 
dose and (2) the relation between dose rate and mortality and hematological 
responses during continuous exposure to death. 



LD 50 / 60 AS A FUNCTION OF DOSE RATE 

The LD 50 / 60 for animals exposed to high dose rates is of interest from two 
standpoints: Lethality does appear to vary with dose rate even within the range 
of high dose rates usually described as "acute," and the response to 
high-dose-rate exposure is used as the standard against which responses to 
low-dose-rate exposure are compared. For example, one standard way of 
comparing recovery after, or even during, a low-dose-rate exposure is to compare 
the LD 50 / 6 o at a ni gh dose rate in animals previously exposed at the low dose 
rate with that of previously unexposed, comparable animals. The difference 
between the two LD 50 /6o' s ls considered to represent the residual injury 
remaining from the initial low-dose-rate exposure, and the difference subtracted 
from the dose given at the low dose rate represents the amount of recovery that 
has occurred. 

Figure 1 summarizes the available information on LD 50 / 60 in sheep 
(California-bred wethers) exposed to dose rates ranging from 30 to 660 R/hr 
(midline air). All exposures were bilateral (1 MVp X ray) or quadrilateral 
( 60 Co), and the two types of radiation sources have been shown to have similar 
depth-dose characteristics. The data from Refs. 2, 3, and 7 were included in 
Page's 1969 presentation. Since that time there have been five more determina- 
tions of the LD 50/60 at dose rates in excess of 30 R/hr— two at SRI, two at 
NRDL, 4 ' 5 and one at the Air Force Weapons Laboratory. 6 The composite of 
the data of Hanks et al. reported in 1966 and the data of some additional groups 
reported in 1969 by Taylor et al. 3 changed the original estimate of 252 R to 
258 R. One can question whether the 30 R/hr value of Page et al. is a part of the 
high-dose-rate continuum. It is included here because the exposures took less 
than a day and because its fit with the protracted dose-rate LD 50 /60 data to be 
considered is even less apparent. When plotted on a graph, these nine data points 
appear to be adequately fitted by a linear regression (correlation coefficient, 
—0.82) expressed by 

Y = 356-0.156 X (1) 



226 



JONES 



400 



350 



300 — 



250 



200 




100 



200 



300 



400 



500 



600 



700 



DOSE RATE, R/hr 



Fig. 1 Relation between LD 50 /60 (midline air) and dose rate in sheep exposed 
at a high dose rate. 



where Y is the LD 50 /60 m roentgens and X is the dose rate in roentgens per hour. 
Since the 95% confidence interval of the slope (0.093) is less than the computed 
slope itself (0.156), there is a significant variation of LD 50 /60 with variation in 
dose rate. Thus, even at dose rates in the so-called acute range, it appears that we 
should specify the dose rate precisely when describing the LD 50 /6o> an d, m using 
acute dose-rate responses to evaluate injury accumulation and recovery at 
protracted dose rates, we should take into account this variation. 

Figure 2 summarizes the presently available LD 50 /6o information for pro- 
tracted dose rates where the exposure time is of the order of days or weeks. 
Results of the work by Jones and Krebs, which is currently in progress at SRI, 
are not sufficient to provide any reliable estimate of the confidence limits for 
the computed LD 50 /60 at 0.84 R/hr, since there were only three deaths among 
the five groups of 12 animals exposed. The computed LD 50 /6o of 1084 R is 
based on one death after exposure at 777 R, one at 837 R, and two at 897 R 
(the highest dose tested). Evaluation of the characteristics of the relation 
between dose rate and LD 50 /6o from about 4 R/hr on down appears to be 
unwarranted until further information is acquired. That there is a tremendous 



RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 227 



1200 



1000 



£ 800 
o 



600 



400 



Jones and Krebs, 
1970 



f 



Page et al. 
1968 



I 



0.5 1.0 1.5 2.0 2.5 

DOSE RATE, R/hr 



3.0 



3.5 



4.0 



Fig. 2 Relation between LD5o/6o( m idline air) and dose rate in sheep exposed 
at a low dose rate to Co gamma radiation. 



change in LD50/60 as compared with acute dose rates is, of course, quite 
apparent. It may even be that below some dose rates (presumably less than 
1 R/hr) the conventional statistics relating exposure dose and mortality do not 
apply. 



CONTINUOUS EXPOSURE TO DEATH 



Figure 3 summarizes lethality and exposure data for the two relatively recent 
studies of lethality and hematologic changes during continuous (23 hr/day) 
protracted exposure to death. The first of these was done by Still et al. 8 at 
NRDL, and the second was done at SRI. At 1.96 R/hr the first death occurred 
on the 25th day of exposure, the median survival time was 42.5 days, and the 
last animal died on day 60. Deaths were spread out more or less uniformly 
throughout the period from days 25 to 60. At 3.79 R/hr, however, there was a 
marked difference in the lethality pattern. The first death occurred slightly 
earlier, on day 22, and all the remaining animals died within the next 6 days, the 
median survival time being 24.5 days. With continuous exposure to death, we are 
always faced with the concept of irradiation after accrual of a dose lethal to the 
individual animal. From Fig. 3 it appears that the effect of this so-called "wasted 
radiation" is a function of the dose rate. At 3.79 R/hr, further exposure after 
accrual of a potentially lethal dose results in a compression of survival time. It is 
as though at this dose rate there are no "low-lethal" doses, and animals die with 
survival times similar to those observed after doses in the high-lethal range for 
acute exposure. For example, the work of Page et al. 7 indicates that the LD50/60 
for terminated exposure at 3.6 R/hr is 495 R. In continuous exposure at 
3.79 R/hr, this dose was accrued in 5.7 days. Subtracting this from the mean 
survival time of 24.7 days gives a survival time after accrual of an LD 50 /6o of 



228 



JONES 



3000 




20 30 40 

DAYS OF EXPOSURE 



50 



60 



Fig. 3 Cumulative mortality and dose in sheep exposed continuously 
(23 hr/day) until death at 1.96 or 3.79 R/hr (midline air). Values for 
1.96 R/hr are estimated from the data of Still et al. 



19 days. This is approximately the vaiue that is typical of survival time when the 
exposure is near the LD 50 /6o f° r dose rates of the order of 450 to 600 R/hr. In 
continuous exposure at 1.96 R/hr, however, there is no discernible compression 
of the range of survival times. Again, Page et al. 7 found that the LD 50 /60 f° r 
2.0 R/hr (terminated exposure) is 637 R. At 1.96 R/hr this dose is accrued in 
14.1 days. Subtracting this value from the mean survival time of 42.9 gives a 
mean survival time after accrual of an LD 50 /6o of 28.8 days. This is somewhat in 
excess of the expected mean survival time with exposure at a high dose rate. 
Thus, although the pattern of lethality with exposure at about 4 R/hr bears 
some analogy to that seen in acute-dose-rate exposure, survival times at about 
2 R/hr present a different pattern. 

In our continuous-exposure study at 3.79 R/hr, we took weekly blood 
samples of all animals beginning on day 9. In our terminated-exposure study at 



RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 229 

0.84 R/hr, we took weekly samples during exposure from the highest dose group 
beginning on day 6. These data are summarized in Figs. 4 to 7, together with 
weekly values beginning with the seventh day of exposure estimated from the 
graphs of Still et al. for their continuous 1.96 R/hr study. In considering these 
data, we should remember that at 1.96 and 3.79 R/hr animals were dying during 
the period under examination but at 0.84 R/hr there were no deaths during 
exposure (the two animals of this group which ultimately died survived 22 and 
39 days after the last blood sample taken during exposure). 




16 20 24 28 
DAYS OF EXPOSURE 



32 



36 



Fig. 4 Values for circulating erythrocytes in sheep during protracted expo- 
sure to Co gamma radiation. Values for 1.96 R/hr are estimated from the 
data of Still et al. • 0.84 R/hr; A, 1.96 R/hr; ■. 3.79 R/hr. 



The erythrocyte data for the three studies are shown in Fig. 4. For all three 
dose rates, there was little appreciable change in red cell count during the first 
three weeks of exposure. At 3.79 R/hr there was a slight decrease at the fourth 
week, when half the animals had already died. At 1.96 R/hr this decrease 
continued during the next three weeks. The red cell count was slightly depressed 
during the last week of exposure at 0.84 R/hr. Apparently at 3.79 R/hr lethality 
occurs before the peripheral red cell count responds to depressed erythroid 
activity in the bone marrow, whereas at 0.84 R/hr the injury accrual rate is too 
slow to be reflected in the peripheral circulation during the 6 weeks of exposure 
(red cell counts in this group do show a decrease beginning in the third week 
after the termination of exposure). Exposure at 1.96 R/hr appears to result in 
the proper combination of an injury accrual rate high enough and a survival time 
long enough for depressed red cell counts to be observed. 

Total peripheral leukocyte counts are summarized in Fig. 5. Here the pattern 
among the three studies shows a distinct dose-rate effect. At all three dose rates, 
there was a definite decrease in total leukocyte count by the first observation 
after the beginning of exposure, the magnitude of depression being directly 
related to the dose rate. This initial decrease was followed by a small additional 
depression at the second observation a week later in all three groups. At the two 
higher dose rates, there was a further depression in leukocyte count, terminal 
values being of the order of 13% of the preirradiation level. At 0.84 R/hr the 



230 



JONES 



i — i — i — i — i — i — r 




j L 



j i i L 



12 16 20 24 28 32 
DAYS OF EXPOSURE 



36 40 44 



Fig. 5 Values for circulating total leukocytes in sheep during protracted 
exposure to Co gamma radiation. Values for 1.96 R/hr are estimated from 
the data of Still et al. •, 0.84 R/hr ; A 1.96 R/hr ; ■, 3.79 R/hr. 



second depression in total leukocytes occurred later, and the final values during 
exposure were about twice those observed at 1.96 and 3.79 R/hr. 

Obviously, changes in total leukocyte counts represent the summation of 
changes in the myeloid and lymphoid leukocytes. In our work we differentiate 
the leukocytes only on the basis of whether they are granulocytic or 
mononuclear cells. For sheep about 85% of granulocytic cells are neutrophils, 
and 90% of mononuclear cells are lymphocytes. When we examine the changes 
in these two categories of leukocytes, w T e find that the dose-rate dependency 
described for total leukocytes is still there but that there are differences for the 
two cell categories. 

The values for mononuclear leukocytes are summarized in Fig. 6. At either 
3.79 or 1.96 R/hr, there was a sharp decline in cell count by about the end of 
the first week of exposure. This initial depression was complete at 3.79 R/hr, in 
the sense that the level reached was about 15% of the preirradiation level, but 
at 1.96 R/hr values about 15% of preirradiation levels were reached after about 
3 weeks of exposure. At 0.84 R/hr, values during exposure never declined below 
about 25% of the preirradiation level, and this range of values was reached after 
about 3 weeks of exposure. With respect to mononuclear leukocytes, then, there 
appears to be a fairly discrete dose-rate dependency with respect to the extent of 
depression and the time of minimum values. 

It has been noted before that changes in circulating lymphocytes following 
whole-body irradiation initially reflect primarily the high radiosensitivity (and 
consequent death) of circulating lymphocytes and then reflect the decreased 



RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 231 




16 20 24 28 32 36 40 44 
DAYS OF EXPOSURE 

Fig. 6 Values for circulating mononuclear leukocytes in sheep during 
protracted exposure to Co gamma radiation. Values for 1 .96 R/hr are 
estimated from die data of Still et al. •, 0.84 R/hr ; A, 1.96 R/hr ; ■ 3.79 R/hr. 



output of the radiosensitive stem eell system of the bone marrow. Although 
originally derived for acute irradiation in small animals, this rationale appears to 
describe satisfactorily the changes in mononuclear leukocytes of the sheep 
discussed here. 

The data for granulocytes are shown in Fig. 7. At 3.79 R/hr there was about 
a 50% depression by the end of the first week of exposure, no further decrease 
during the next week, and then a final depression to near-zero values during the 
next week in the animals surviving long enough to be assayed. At each of the 
two lower dose rates there was a slight depression in granulocytic cell count after 
about a week of exposure, then a slight rise during the next week. At 0.84 R/hr 
this "rebound" persisted for another week. After the apparent abortive rise, 




12 



16 20 24 28 
DAYS OF EXPOSURE 



32 



36 



40 44 



Fig. 7 Values for circulating granulocytes in sheep during protracted expo- 
sure to ^ Co gamma radiation. Values for 1.96 R/hr are estimated from die 
data of Still et al. •, 0.84 R/hr ; A, L96 R/hr ; ■, 3.79 R/hr. 



232 JONES 

granulocytic cell count decreased over the next 2 weeks at both of the lower 
dose rates. At 1.96 R/hr, values less than 20% of preirradiation levels were 
observed during the final 3 weeks of observation. At 0.84 R/hr the maximum 
depression was only to about 50% of the preirradiation value. 

In addition to higher radioresistance of circulating granulocytes, as compared 
with lymphocytes, there is also a considerable reserve of neutrophils available for 
release into the circulation. For example, Page et al. 9 recently reported that in 
unirradiated sheep circulating granulocytic cells increase over 300% within a day 
of injection of endotoxin. As noted by Still et al., 8 these two factors could 
account for the chronologic delay in the decrease in circulating granulocytic cells 
of the sheep during continuous irradiation at doses of 1.96 or 0.84 R/hr. Still 
et al. 8 also noted that the major point to be made from studies of continuous 
chronic exposure of large animals was that, unlike the rat, large animals appear 
unable to adapt to low-level whole-body gamma irradiation. This conclusion 
obviously appears valid at dose rates of 1.96 R/hr and up. As for lower dose 
rates, although there was no discernible change in the granulocytic cell count 
during the last 2 weeks of exposure at 0.84 R/hr (Fig. 7), further decreases have 
been observed during postexposure observation of these animals (now in 
progress). This finding, together with the fact that some deaths did occur after 
exposure, indicate that, although the sheep may be capable of some transient 
adaptation during protracted exposure, injury does accrue even at a dose rate 
below 1 R/hr. 



REFERENCES 

1. D. G. Brown, R. G. Cragle, and T. R. Noonan (Eds.), Proceedings of a Symposium and 
Dose Rate in Mammalian Radiation Biology, Apr. 29— May 1, 1968, Oak Ridge, Tenn., 
USAEC Report CONF-680410, UT-AEC Agricultural Research Laboratory, July 12, 
1968. 

2. G. E. Hanks, N. P. Page, E. J. Ainsworth, G. F. Leong, C. K. Menkes, and E. L. Alpen, 
Acute Mortality and Recovery Studies in Sheep Irradiated with Cobalt-60 Gamma Rays 
or 1 MVP X-Rays, Radiat. Res., 27: 397-405 (1966). 

3. J. F. Taylor, E. J. Ainsworth, N. P. Page, and G. F. Leong, Influence of Exposure Aspect 
on Radiation Lethality in Sheep, Report NRDL-TR-69-15, Naval Radiological Defense 
Laboratory, Mar. 24, 1969. 

4. E. T. Still, J. F. Taylor, G. F. Leong, and E. J. Ainsworth, Mortality of Sheep Subjected 
to Acute and Subsequent Protracted Irradiation, Report NRDL-TR-69-3 2, Naval 
Radiological Defense Laboratory, June 9, 1969. 

5. E. T. Still, J. F. Taylor, G. F. Leong, and E. J. Ainsworth, The Influence of the Amount 
of Initial Radiation Exposure on the Recovery Pattern in Sheep, Report 
NRDL-TR-69-97, Naval Radiological Defense Laboratory, July 15, 1969. 

6. T. S. Mobley, E. T. Still, W. Rush, J. F. Taylor, R. L. Persing, and T. C. DeFeo, 
Interlaboratory Comparison of Mortality in Sheep Exposed to Cobalt Radiation, 
Report AFWL-TR-69-48, Air Force Weapons Laboratory, Air Force Systems Command, 
Kirtland Air Force Base, October 1969. 

7. N. P. Page, E. J. Ainsworth, and G. F. Leong, The Relationship of Exposure Rate and 
Exposure Time to Radiation Injury in Sheep, Radiat. Res., 33: 94—106 (1968). 



RESPONSES OF LARGE ANIMALS TO RADIATION INJURY 233 



8. E. T. Still, J. F. Taylor, G. F. Leong, and E. J. Ainsworth, Survival Time and 
Hematological Responses in Sheep Subjected to Continuous Cobalt Gamma Irradia- 
tion, Report NRDL-TR-69-28, Naval Radiological Defense Laboratory, May 9, 1969. 

9. N. P. Page, E. J. Ainsworth, and J. F. Taylor, Residual Injury of the Hematopoietic 
System of X-irradiated Sheep, NRDL-TR Report, Naval Radiological Defense Laboratory, 
July 15, 1969. 



CRITERIA FOR RADIATION INJURY 



JOHN S. KREBS 

Stanford Research Institute, Menlo Park, California 



ABSTRACT 

The nature of radiation injury in animals is considered largely from the viewpoint of 
destruction of radiation-sensitive cells and tissues. The methods for determining the 37% 
survival dose (D37) in animals is reviewed; the limitations of treating cell survival after 
irradiation as an exponential process are considered briefly; and some of the principal results 
on survival of animal cells are summarized. The relation of bone-marrow-cell survival to 
survival or death of the whole animal is considered. In two experimental comparisons the 
LD50 of the animal was predictable from the survival of the bone-marrow cells; in two other 
experimental comparisons there was no relation between stem-cell survival and LD50. The 
rate of replacement of the bone-marrow cells after irradiation is considered briefly. Data 
collected from three independent sources gave a mean cell doubling time of 1.3 3 days 
(range, 0.96 to 1.7) for replacement of bone-marrow cells of rats and mice. There was no 
significant delav in initiation of recovery and no evident relation between cell doubling time 
and radiation dose. 



The title "Criteria for Radiation Injury" suggests to me a large body of ideas, 
knotty problems, frustrations, and past confusions. From this somewhat 
amorphous mass of thought, there emerges a small group of propositions that I 
think can be called the principal driving forces of the problem of radiation 
injury. 

First, the study of radiation injury actually implies the study of quantity of 
injury, methods for measuring injury, and identification of exposure conditions 
that may modify the kind or degree of injury. I note that this subject tends to 
come up before the nature or definition of radiation injury is even established. 
This leads to the second proposition: When we are primarily concerned with 
measurement of injury, the injury is defined strictly in terms of the experiment 
and the biological end point used to measure it. The third proposition is that 
adequate study of radiation injury requires the study of repair of injury if an 
adequate understanding of the biological meaning of injury is to be obtained. 

234 



CRITERIA FOR RADIATION INJURY 235 

In general, three types of biological end points have been used in the study 
of radiation injury: first, a change in some kind of physiological function or 
performance capacity; second, a loss or destruction of radiation-sensitive cells or 
tissues; and, third, a total-failure type of response, such as death or incapacita- 
tion. General biological theory holds that these three end points are mutually 
related by causal chains from the primary radiation events, but in practice the 
interrelations are often hard to draw without considerable unsupported 
speculation. In this review I have concentrated primarily on the second type of 
biological end point and will consider radiation injury and repair largely in terms 
of loss and replacement of tissue, with some remarks on the relation between 
tissue loss and biological failure, i.e., death. 

RADIATION INJURY AS A DESTRUCTION OF 
SENSITIVE CELLS AND TISSUES 

The modern study of radiation injury as a destruction of sensitive cells and 
tissues began about 10 years ago with the development of methods for in vivo 
measurement of the relative number of stem cells of bone marrow. These are 
cells that are capable of (1) self-replication and (2) differentiation into 
intermediate and final stages of formed elements of blood. Our present concept 
is that much of the significant radiation damage to bone marrow involves 
destruction of the stem cells and a consequent loss of the source of formed 
elements of blood. 

The two methods for measuring stem cells in bone marrow are the 
colony-forming unit (CFU) of Till and McCulloch 1 and the erythropoietin- 
response technique of Gurney, Lajtha, and Oliver. 2 The first technique involves 
injecting a counted number of mouse bone-marrow cells into a lethally irradiated 
recipient mouse and counting the number of hemopoietic colonies that have 
developed in the spleen of the recipient mouse 8 to 10 days later. The second 
technique involves infusing an animal with erythrocytes until the hematocrit 
rises and erythrocyte production in the bone marrow ceases. The stem cells can 
then be stimulated by injection of erythropoietin to produce more erythrocytes, 
and the response can be measured by studying incorporation of 5 Fe into 
circulating erythrocytes. In both types of study the effect of radiation is 
expressed as a survival fraction (S/S ), i.e., the fraction of the response of 
unirradiated animals in relation to radiation dose. 

The result of a study of erythropoietic-stem-cell response in mice exposed to 
250-kVp X rays is illustrated in Fig. 1. Here the fraction of surviving erythroid 
stem cells is plotted on a logarithmic scale against radiation dose, and an 
apparent straight line is obtained. For reasons of mathematical convenience, this 
line is characterized by two parameters: the apparent survival at zero dose, called 
the extrapolation number, and the 37% survival dose, called the D 37 . 

Each of the points in Fig. 1 represents the survival fraction of a group of five 
mice at the indicated dose, and the whole figure is the pooled result of 10 or 12 



236 



KREBS 



o 





I 

• 

\5 . 


I 


I 


I 


I 




1.0 










— 




I\ 


t 


i\ 








0.1 






• 


• 


• 
\ • 

• 


: 


)01 


I 


I 


I 


I 


I 


• 



50 100 150 200 250 

RADIATION EXPOSURE, R 



300 



Fig. 1 Survival of erythropoietic-stem-cell response in mice as a function of 
dose of 250-kVp X rays. 

experiments. Three comments can be made: First, the set of experiments as a 
whole can be fairly represented by a straight line on semilogarithmic paper, with 
an extrapolation number of 1.2 and a D 37 of 71.5 R. Second, the deviations of 
the points from the line are quite large, amounting at some of the doses to as 
much as 50 R of radiation exposure. Third, at the 25-R dose all the points show 
an increased survival above control values, as if the radiation had a stimulating 
effect on erythroid-stem-cell proliferation. The overall conclusion is that the 
effect of radiation on erythroid stem cells is a complex process in which 
destruction of the cells at an exponential rate is the principal result readily 
apparent over a sufficient range of doses but in which a number of other events 
also occur. 

Similar results can be obtained by using the CFU technique mentioned 
previously. In addition, methods have been developed to study the radiation 
response of germinal cells of skin and intestinal epithelium. In these latter 
experiments it has not been possible to determine an extrapolation number, but 
values of D 3 7 have been obtained. All methods involving in vivo measurement of 
stem or germinal cells are subject to numerous untested assumptions, but they 
all seem to give exponential survival curves over a reasonable dose range. 

This type of study of injury is not necessarily confined to cells. Figure 2 
illustrates the relation between weight of the testes of mice and radiation dose at 



CRITERIA FOR RADIATION INJURY 



237 



200 




1 00 200 300 

X-RAY DOSE, rads 



400 



Fig. 2 Weight of testes of mice at 28 days after exposure to 250-kVp X rays 
as a function of radiation dose. 



28 days after exposure to 250-kVp X rays. It can be seen that the testes' weight 
falls to a minimum value as the dose increases; this minimum value can be taken 
to be the weight of the nonsensitive structural portion of the tissue. When this 
nonsensitive weight is subtracted from the whole-testes weight at each dose and 
the fraction of radiosensitive weight remaining is plotted on a logarithmic scale 
against radiation dose, again a reasonably straight line is obtained, as shown in 
Fig. 3. The line shown has an extrapolation number of 1.0 and a D 37 of 78.9 
rads. It can be inferred that the involution of the testes following irradiation 
reflects the loss of stem cells (type A spermatogonia) from the testes. 

A similar study has been done using loss of weight of the spleen in mice after 
irradiation. In this study there was also an exponential decrease in the survival of 
the radiosensitive portion of the spleen with increasing radiation dose. Similar 
studies can also be done with weight of mouse thymus or with DNA content of 
mouse bone marrow or spleen. In fact, I suspect that with some patience and 
imagination the radiosensitivity of a number of proliferative tissues in several 
animal species could be investigated. 

Table 1 contains a brief list of values of D 37 obtained for several cell lines 
and tissues exposed to X rays. The list is in no sense complete and is intended to 
indicate the level of radiosensitivity that may be expected from acutely 
proliferating cells and tissues of mammals. All measurements but the last were 
made in vivo with the techniques mentioned before. The last item, human liver 
cells, measured by using a cell-culture technique in vitro, is included to indicate 
that the radiosensitivity of human (and presumably other large mammal) cells is 
not grossly different from that of rats and mice. 



238 



KREBS 




0.01 



100 200 300 

RADIATION DOSE, rads 



400 



Fig. 3 Survival of the radiosensitive portion of mouse testes weight as a 
function of dose of 250-kVp X rays. 



The values of D 3 7 shown in Table 1 range from 54 to 160 R; most of the 
values fall between 70 and 120 R. At the present time this table seems to be a 
fair summary' of the radiosensitivity of actively proliferating normal cells and 
tissues of animals. Radiation injury in the sense of destruction of radiation- 
sensitive cells and tissues, then, involves an exponential survival of the sensitive 
cells and tissues, with 3 7% of the tissue remaining for each increment of 70 to 
120 rads. 

RELATION BETWEEN CELL DESTRUCTION AND ANIMAL SURVIVAL 



Given that we have some prediction of the sensitivity of cells to radiation, 
the question of greater interest is whether functional loss, incapacitation, or 
death of the animal can be related to the destruction of the cells. The data on 
this question are still somewhat limited, but a few direct comparisons are 
available for animal lethality. 

The most direct comparison we can make is that between the 30-day LD 5 
in mice and the survival of stem cells of the bone marrow at the LD 5 dose. The 



CRITERIA FOR RADIATION INJURY 



239 



Table 1 

D 37 FOR VARIOUS CELLS AND TISSUES EXPOSED 
TO X RAYS 



Cell or tissue 


Animal 


D37 


Reference 


Erythropoietic 








stem cell 


Mouse 


65 rads 


10 


Erythropoietic 








stem cell 


Mouse 


HOrads 


2 


Erythropoietic 








stem cell 


Mouse 


71 R 


11 


Bone-marrow CFU 


Mouse 


77 R 


5 


Spleen CFU 


Mouse 


54 R 


5 


Erythropoietic 








stem cell 


Dog 


66 R 


12 


Testes weight 


Mouse 


79 R 


13 


Testes weight 


Mouse 


102 R 


14 


Testes weight 


Rat 


160 R 


14 


Testes weight 


Hamster 


160 R 


14 


Spleen weight 


Mouse 


140 R 


11 


Germinal layer 








of skin 


Mouse 


135 rads 


3 


Intestinal 








epithelium 


Mouse 


97 rads 


4 


Liver cells 








(tissue culture) 


Human 


119 rads 


15 



test system is one in which the LD 50 can be altered in some way, e.g., by 
protection or by changing the dose rate or the type of radiation. The 
stem-cell-survival curve and the LD 50 are determined for two conditions in 
which the LD 50 values will be different, and the survival fraction of stem cells at 
the LD 50 is calculated for each condition. If the survival fraction of stem cells is 
the same at both values of LD 50 , this constitutes support for the hypothesis that 
death of an animal is caused by the reduction of the bone-marrow stem cells 
below some critical number. 

A set of analyses of this type is shown in Table 2. The first part of the table 
summarizes the work of Ainsworth and Larsen 5 on the relation of bone-marrow 
colony-forming units and LD 50 in normal mice and in mice protected with AET 
(2-aminoethylisothiouronium bromide hydrobromide). The AET increased the 
LD 5 by 80%, but the survival fraction of colony-forming units in bone marrow 
at the AET LD 50 was nearly the same as at the untreated LD 50 . The predicted 
LD 5 is the dose at which the survival of CFU's in mice protected with AET was 
exactly the same as the survival of CFU's in unprotected mice at their LD 50 . 
The predicted and measured LD 50 's are quite close together, and the results 
imply that lethality in the mouse is determined in this case by survival of CFU's. 



240 KREBS 

Table 2 



LD 50 VS. SURVIVAL OF BONE-MARROW STEM 
CELLS 

Colony-Forming Units in Mice Treated with AET 

Control AET treated 



LD50 


721 R 


1313 R 


Stem cell D 37 
S/S at LD 50 


77 R 

1.5 x 10~ 4 


128 R 
0.84 x 10" 4 


Predicted LD 50 




1240 R 



Erythropoietic Stem Cells in Mice Irradiated with 
X Rays or Neutrons 

250-kVp X rays Fission neutrons 



LD50 


880 R 


384rads 


Stem cell D37 


71.5 R 


27.8 rads 


S/S at LD 50 


5.46 x 10 6 


1.84 x 10 6 


Predicted LD 50 




3 54 rads 



Colony-Forming Units in Mice Irradiated at Different 
Dose Rates 



60 Co (1700 R/hr) 60 Co (200 R/hr) 



LD 50 


896 R 


1408 R 


Stem cell D37 
S/S at LD 50 


96.3 R 
1.31 x 10" 4 


116.1 R 
7.32 x 10"* 


Predicted LD 50 




1073 R 



The second part of the table shows a similar type of comparison for 
erythropoietic stem cells in mice irradiated with 250-kVp X rays or with fission 
neutrons. The results are from my own data, partly unpublished. The difference 
in LD 50 was more than a factor of 2, but again the survival fractions of stem 
cells at the respective LD 50 's were reasonably close. The predicted LD 50 
differed from the measured LD 50 by only 30 rads, and these results confirm 
those of Ainsworth and Larsen. The third part of the table shows still another 
comparison of colony-forming units in mice irradiated with 60 Co at two 
different dose rates (these are unpublished results of D. C. L. Jones and myself). 
Decreasing the dose rate from 1700 R/hr to 200 R/hr increased the LD 50 by 
more than 50%. In this case, however, there was a substantial difference in the 
survival fraction of the colony-forming cells at the LD 50 's for the two dose 
rates, and the survival of the cells in this case appears to be a poor predictor of 



CRITERIA FOR RADIATION INJURY 241 



Table 3 

COMPARISON OF ENDOGENOUS COLONY-FORMING UNITS AND 
LD 50 FOR MICE WITH GENETIC DIFFERENCES IN LD 50 









Dose for 1 






LD 50 , 


D 3 7 of CFU* 


CFU/mouse, 


CFU/lOOmice 


Mouse strain 


R 


R 


R 


at the LD50 


BALB/cJ 


616 


79.4 


475 


16.9 


SWR/J 


646 


57.1 


683 


191.0 


C57BL/6J 


705 


65.0 


638 


35.7 


CBA/J 


725 


76.1 


616 


23.8 


C57BR/edJ 


777 


83.8 


720 


50.6 






the LD 50 . We still consider these results provisional, but the third result implies 
that factors other than stem-cell survival may exercise substantial control over 
death of the animal. 

Results of a related study by Yuhas and Storer 6 using inbred strains of mice 
with genetically determined differences in LD 5 and comparing the LD 50 with 
the dose and response relation for endogenous colony-forming units in the 
strains of mice are shown in Table 3; the original data have been converted to a 
form easily comparable with the previous results in Table 2. The second column 
of Table 3 lists the X-ray LD 50 's of the various strains of mice, and the last 
column shows a calculation of the number of colonies per 100 spleens expected 
at the LD 50 for the various strains. This calculation is equivalent to the 
calculation of survival fraction of stem cells at the LD 5 in the other studies. It 
can be seen that there is no relation in these strains of mice between the LD 50 
and the survival of stem cells at the LD 50 . This is in agreement with the studies 
on dose rate and in contrast to the studies on AET protection and 
neutron— X-ray irradiation. 

The conclusion, then, is that survival of bone-marrow stem cells is an 
important but not an exclusive determiner of the lethal radiation dose to the 
animal and that other factors not yet determined also have a significant effect on 
lethal dose. The evidence that stem-cell survival does not constitute the sole 
determinant of animal lethality has important implications for the development 
of methods of treating lethal radiation injury. 



REPAIR OF RADIATION INJURY: REPLACEMENT OF 
DESTROYED TISSUE 

The ability of an animal to repair radiation injury implies eventually a 
replacement of the destroyed stem cells and tissues by accelerated proliferation 
of cells or reduced utilization and destruction of cells, or both. Because of the 



242 



KREBS 



nature of cell division, we tend to expect that the cell or tissue replacement wil 
follow an exponential course of the form 



log X = kt 



(1) 



where X is the quantity of cells or tissue at time t and k is a growth-rate constant 
representing the net fractional gain of cells or tissue per unit time. The constant 
k can be determined by plotting log X against t, and a more convenient form of 
representation of k is 0.301/k, which is the doubling time of the cells. 

Figure 4 shows values for surviving percentage of colony-forming units in the 
mouse plotted on a logarithmic scale against time after exposure to 450 R of 
X rays. The data, which are taken from the work of Hanks and Amsworth, 7 have 
been fitted by a line of the form of Eq. 1 for the points between 1 and 11 days 
after irradiation. It can be seen that the data are reasonably fitted by the 
calculated line, considering the inherent variation of the data. The doubling time 
obtained for the fitted line was 1.3 3 days, or 31.9 hr. This doubling time is 
about twice the minimum generation time expected for cells of the bone marrow 
and probably represents a balance between the generation time for the 
colony-forming cells and the loss of colony-forming cells by differentiation to 



uuu 




1 I 


1 


1 


1 ' 


! ! I 


! — 


100 


=- 










y% 


/ i 


10 


=- 


• / 


• / 


• J 


/• 




-= 


1 


= 


'• 










E 


01 


I 


1 1 


1 


1 


1 1 


i i i 





4 8 12 

TIME AFTER EXPOSURE, days 



Fig. 4 Return of colony-forming units in the bone marrow of the mouse with 
time after exposure to 450 R of X rays. 



CRITERIA FOR RADIATION INJURY 



243 



more specialized types. Inspection of the fitted line indicates that cell 
replacement begins effectively at about 1/2 day after irradiation and recovery to 
100% of the initial value is accomplished in 11.7 days. 

The process of cell doubling does not continue indefinitely. As the value of 
X approaches the normal size or amount of tissue present in the unirradiated 
animal, the rate of growth slows and eventually stops at some steady state. In 
this region of repair the events are quite complex. Sometimes the number of 
cells exceeds the control value, as indicated in Fig. 4 at 14 days; sometimes the 
cell count settles at a value less than the control value; and sometimes the cell 
count goes through several oscillations above and below the control value. In 
general, the events in the region near 100% repair of tissue destroyed by 
radiation are not amenable to systematic analysis. 

Some analysis can be done by using the empirical time point at which the 
radiation-damaged tissue comes to the level of 50% of the control value. For this 
purpose I have used the data on replacement of erythropoietic stem cells of the 
rat from Baum, Wyant, and Vagher 8 and the data on total bone-marrow DNA 
(which is a measure of cell count) from Davis and Cole. 9 The data are 
summarized in Table 4. The initial survival percentage was obtained from the 
data in the case of Baum et al. and was estimated by assuming a D 3 7 of 80 rads 
in the case of Davis and Cole. The number of cell doublings to return the initial 
survival value to 50% of control was calculated from the initial survival, and the 
time to return to 50% of control was obtained from the data. The ratio of these 
values is the cell doubling time, shown in the last column in the table. The values 
for cell doubling time ranged from 0.96 to 1.72 days, and the mean doubling 
time was 1.3 3 days, precisely the value obtained from the data of Hanks and 
Ainsworth. 7 



Table 4 

TIMES FOR REPAIR OF RADIATION-DESTROYED BONE 
MARROW TO 50% OF CONTROL VALUE 











Observed 


Calculated 








Number 


repair 


cell-doubling 


Tissue 


Dose, 




of cell 


time, 


time, 


measurement 


R 


S/S 


doublings 


days 


days 


Erythropoietic 


150 


0.356 


0.49 


0.8 


1.64 


stem cells 


200 


0.166 


1.59 


1.95 


1.23 




2 50 


0.074 


2.76 


3.0 


1.09 


Bone-marrow 


270 


0.034 


3.88 


3.72 


0.96 


total DNA 


390 


0.0076 


6.04 


7.74 


1.28 




48 5 


0.00236 


7.73 


13.3 


1.72 




540 


0.00118 


8.73 


12.13 


1.39 



244 KREBS 

It appears, then, that rats and mice are able to rapidly replace bone-marrow 
cells destroyed by irradiation. The doubling time for replacement of such cells is 
about 32 hr, and the rate does not appear to depend on radiation dose. 
Considering the variety of sources of the data and the initial purposes of the 
experiments, the agreement is rather surprising. A number of obvious specula- 
tions could be made about the nature of cell replacement in other species, the 
possibility of modifying the replacement rate by drugs or other treatment, and 
the role of cell-replacement rate in determining the survival of the animal. These 
speculations are properly the source of ideas for future experimental investiga- 
tion. 



REFERENCES 

1. E. A. McCulloch and J. E. Till, The Radiation Sensitivity of Normal Mouse Bone 
Marrow Cells, Determined by Quantitative Marrow Transplantation into Irradiated Mice, 
Radiat. Res., 13: 115-125 (1960). 

2. C. W. Gurney, L. G. Lajtha, and R. Oliver, A Method for Investigation of Stem-Cell 
Kinetics, Brit. J. Haematol., 8: 461-466 (1962). 

3. H. R. Withers, The Dose— Survival Relationship for Irradiation of Epithelial Cells of 
Mouse Skin. Brit. J. Radiol., 40: 187-194 (1967). 

4. II. R. Withers and M. M. Elkind, Radiosensitivity and Fractionation Response of Crypt 
Cells of Mouse Jejunum, Radiat. Res., 38: 598-613 (1969). 

5. E. J. Ainsworth and R. M. Larsen, Colony-Forming Units and Survival of Irradiated Mice 
Treated with AET or Endotoxin, Radiat. Res., 40: 149-176 (1969). 

6. J. M. Yuhas and J. B. Storer, On Mouse Strain Differences in Radiation Resistance: 
Hematopoietic Death and the Endogenous Colony-Forming Unit, Radiat. Res., 39: 
608-622 (1969). 

7. G. E. Hanks and E. J. Ainsworth, Repopulation of Colony-Forming Units in Mice, 
Nature, 215: 20-22 (1967). 

8. S. J. Baum, D. E. Wyant, and J. P. Vagher, Comparative Hematopoietic Cytokinetics in 
Rats Exposed to Either 250 kvp X Ray or Mixed Gamma— Neutron Radiation, Report 
AFRRI-SR-68-2, Armed Forces Radiobiology Research Institute, January 1968. 

9. W. E. Davis, Jr., and L. J. Cole, Comparative Effects of Fast Neutrons and X-Rays on 
Marrow Deoxyribonucleic Acid (DNA) Content in Mice, Radiat. Res., 14: 104—116 
(1961). 

10. R. Alexanian, D. D. Porteous, and L. G. Lajtha, Stem-Cell Kinetics After Irradiation, 
Int. J. Radiat. Biol., 7: 87-94 (1963). 

11. J. S. Krebs, Stanford Research Institute, unpublished data. 

12. R. J. Holloway, M. L. Albright, G. F. Leong, J. S. Krebs, and E. L. Alpen, Stem Cell 
Migration and Radiosensitivity in the Bone Marrow of the Dog, Report 
NRDL-TR-69-98, Naval Radiological Defense Laboratory, July 1969. 

13. J. S. Krebs, Analysis of the Radiation-Induced Loss of Testes Weight in Terms of Stem 
Cell Survival, Report NRDL-TR-68-104, Naval Radiological Defense Laboratory, 
September 1968. 

14. H. I. Kohn and R. F. Kallman, Testes Weight Loss as a Quantitative Measure of X-Ray 
Injury in the Mouse, Hamster, and Rat, Brit. J. Radiol, 27: 5 86-591 (1954). 

15. D. L. Dewey, Effect of Oxygen and Nitric Oxide on the Radiosensitivity of Human Cells 
in Tissue Culture, Nature, 186: 780-782 (1960). 



SPECIES RECOVERY 
FROM RADIATION INJURY 



J. F. SPALDING and L. M. HOLLAND 

Biomedical Research Group, Los Alamos Scientific Laboratory, University of California, 

Los Alamos, New Mexico 



ABSTRACT 

The acute dose of gamma radiation required to produce death of livestock may range from 
as little as 300 to as much as 800 rads. All mammalian species have a recovery capability or 
an increased tolerance, or both, to protracted radiation which is not necessarily related to 
the acute lethal dose for the species. Recovery from single acute or protracted nonlethal 
exposures may be expected within 90 to 120 days in most mammalian species, leaving no 
irreparable somatic lesion of consequence to livestock. Transient or permanent sterility may 
be caused in some mammalian species by nonlethal doses of radiation. However, hereditary 
radiation-induced genetic injury following nonlethal exposures to ionizing radiation should 
not be of serious concern to livestock breeders. 



In the event of nuclear war, all life on earth would be exposed to increased levels 
(above normal background) of ionizing radiation and might suffer some degree 
of radiation injury. Living organisms in or near high-priority target areas would 
be subjected to more-intense exposure and thus would die or would suffer from 
delayed radiation effects from serious but nonlethal exposures. It is perhaps 
ironical, but nonetheless true, that the most technically and culturally advanced 
societies would suffer the greatest impact of a nuclear war, for, in effect, the 
creation would attempt to paralyze and destroy its creators. The degree to which 
a target society can survive a nuclear weapon attack is directly related to its 
knowledge and understanding of the effects and limitations of ionizing radiation. 
This presentation, as its title suggests, concerns some aspects of recovery in 
mammals exposed externally to serious but nonlethal levels of ionizing 
radiations. Because livestock are the mammals of interest at this symposium, 
emphasis is on natural recovery from radiation injury without therapy. 

245 



246 SPALDING AND HOLLAND 

LETHAL AND IMONLETHAL EXPOSURES 

Since this discussion is concerned primarily with mammalian recovery from 
radiation injury, lethality is only briefly considered. Figure 1 clearly illustrates 
that the doses required to kill 50% of the animals within 30 days of exposure 
(LD 50 /3o) differ markedly among species. It is also apparent that wide 
mtraspecies LD 50 / 30 ranges have been reported by different investigators. 1 3 



1000 



800 



2 600 



400 



200 



1 r 



J L 



SHEEP AND f GUINEA 
GOAT PIG 

SWINE DOG 



MAN 1 MOUSE } RAT ] RABBIT f 

BURRO MONKEY HAMSTER OTHER 

MAMMALS 
ANIMAL SPECIES 



Fig. 1 Approximate LD50/30 dose range reported for different mammalian 
species showing intraspecies and interspecies variation. 

From LD 50 / 30 data presently available, one might assume that farm animals in 
general have a relatively low LD50/30 from whole-body short-term (acute) 
exposures of between 300 and 800 rads. Although the species difference in 
LD50/30 1S rea l an d highly significant, no species characteristics such as 
life-span, body weight, and metabolic rate have been shown to relate well to the 
LD 50 / 30 value. It can only be said that survival or death after large acute doses 
of ionizing radiation in a given species is influenced to varying degrees by such 
factors as sex, age, physical fitness, environment, and exposure conditions. The 
ability to tolerate and recover successfully from radiation injury is not unique to 
(or denied to) any one mammalian species. Given the proper recovery 
environment and temporal conditions, all mammalian species have a recovery 
capability. 

CAUSE AND TIME OF DEATH 



Cause of death from whole-body irradiation is generally considered to be a 
function of the total exposure received (dose) and the time span over which the 



SPECIES RECOVERY FROM RADIATION INJURY 



247 



dose was received (dose rate). This relation is illustrated in Fig. 2. Although the 
figure does not show the time span over which the dose was received, a 
survival-time curve for increasing dose rate, which is academic and for 
illustration only, is shown which may or may not represent the actual survival 
time of any single species. Note, however, that serious gastrointestinal or 
cerebral (central nervous system) injury is quite unlikely to be successfully 
repaired. Thus it becomes apparent that discussion of species recovery from 
radiation injury is, for the most part, a discussion of the repair characteristics of 
hematopoietic organs. 



INCREASING DOSE RATE 




100 200 400 800 1600 3200 6400 
DOSE, rads 



Fig. 2 Generalized relation of cause and time of death, dose rate, and 
total-dose whole-body exposure. 



Perhaps the most significant factor involved in species recovery from 
exposure to ionizing radiation is dose rate. The relation between dose rate and 
mean lethal dose or recovery capability as the dose rate progresses from 
protracted or chronic to acute for an animal with an LD 50 /3o oi about 450 rads 
is shown in Fig. 3. Although the degree of this dose-rate effect varies from one 



248 



SPALDING AND HOLLAND 




0.1 



0.5 



5.0 10 50 

DOSE RATE, rads/hr 



00 



500 1000 



Fig. 3 Graphic relation between dose rate and mean lethal dose for a mammal 
with an acute LD50/30 of 450 rads. The acute lethal-dose LD 50/30 is shown 
on the right. As the dose rate changes from acute to chronic effects (right to 
left), the mean lethal dose can be expected to increase. 

species to another, the general dose-rate-effect relation should apply to all 
mammals. 



RATE OF REPAIR AND GENETIC INVOLVEMENT 
OF HEMATOPOIETIC RECOVERY 



Although experience suggests that no mammalian species has been denied 
the capability of repairing radiation injury, there is ample evidence that this 
capability varies widely among species. Variations of repair in mammals have 
been reviewed by Page, 3 who rated several species according to their response or 
recovery capability from protracted radiation exposures. Mice and swine are 
rated as having the most efficient recovery capability, and, as in the case of the 
LD 50 / 30 , there appears to be no easily recognized correlation between repair 
efficiency and phenotypic or genotypic species characteristics. 

Recovery rate of hematopoietic tissue has been shown to be independent of 
size of acute conditioning dose in mice 4 and independent of total accumulated 
dose from continuous exposures. 5 Mice exposed to 60 Co gamma rays at a dose 
rate of 4.5 rads/hr for 188 and 3 55 hr showed similar lag times (approximately 
10 to 12 days) from termination of the gamma-ray stress to the maximum 



SPECIES RECOVERY FROM RADIATION INJURY 



249 



depression in red blood cell count (RBC). Recovery from the point of maximum 
depression to the 50% level was also similar (approximately 7 to 9 days) for the 
two groups in spite of a dose-difference factor of 1.89. 

These observations are shown graphically in Fig. 4. Independence of the 
repair rate of size of protracted gamma-ray dose has also been observed in 
monkeys. Peripheral blood characteristics of monkeys exposed to 500, 750, or 



100 




30 40 

TIME, days 



Fig. 4 Red blood cell (RBC) repopulation in peripheral blood following 
protracted gamma-ray exposure of the mouse. Exposure for all groups was 
started on day 1. The exposure was continued to death for group 1 and was 
terminated after 188 hr for group 2 and after 35 5 hr for group 3. Delayed 
response and recovery are shown for groups 2 and 3 following gamma-ray 
exposure, o, group 1; •, group 2; -, group 3. 



1000 rads of gamma rays during a 10-day period are shown in Figs. 5 and 6. 
Animals receiving 500 rads showed only slightly depressed RBC characteristics; 
however, those exposed to 750 and 1000 rads showed dose-related injury but 
dose-independent recovery (Fig. 5). The lymphocyte response, plotted in Fig. 6, 
also shows dose-dependent response or injury and recover}" rates independent of 
dose. 

Response to radiation injury from protraction of ionizing radiation dose 
varies widely among mammalian species. The degree to which a species responds 
to injury from ionizing radiation is, no doubt, genetically inherent to the given 
species. This genetic influence on radiation resistance may be expressed as 
resistance to or repair of radiation injury. Recent investigations with mice 
suggest that different responses to radiation injury within the same mouse strain 



250 



SPALDING AND HOLLAND 




■10-day exposure 7 



60-day rest phase - 



+ 2nd 30-day H 



performance phase 



J I.... -I 



_i i 1 ■ - ■ ^j i i i i i i i 1 1 1 1 1 1 1 1 — 1 

4 10 14 20 24 30 36 43 50 57 63 71 78 85 95 101 105 116 120 126 

TIME, days 

Fig. 5 Radiation-induced depression and recovery of hemoglobin, packed cell 
volume, and red-blood-cell count in the peripheral blood of monkeys 
following (-^-), 500 (•••••••), 750 (- -a- -), and 1000 (— o — )radsof 

gamma rays protracted over 10 days of exposure. 



may be due to a resistance factor rather than to inherent differences in the rate 
of repair from radiation-induced injury. In Fig. 7 the packed cell volume (PCV) 
from peripheral blood samples of two mouse substrains is plotted during and 
after 21 days of gamma-ray exposure at a dose rate of 4.1 rads/hr. The 
difference in radiation response between the two sublines, as shown in the 
figure, can be attributed to differences in resistance to radiation (either dose rate 
or total dose) rather than to hematopoietic recovery (repair-rate) differences 
between the two substrains. If the LD 50 / 30 method had been used on day 32 
(11 days after exposure, Fig. 7) to determine the repair rate, one might have 
erroneously attributed the substrain difference in response to radiation to highly 
significant differences in repair rate of hematopoietic tissue. This problem may 
exist to some degree in recovery rates reported for different mammalian species 
where the degree of injury in the repair half-time test is assumed to be 



SPECIES RECOVERY FROM RADIATION INJURY 



251 



14,000 



10,000 



4,000 



2,000 — 



I I I I I I I I I I 
10-day exposure 



I I I I I I I I II I 



8,000 —§l— 



6,000 




50 60 70 
TIME, days 



110 120 



Fig. 6 Radiation-induced depression and recovery of lymphocytes in the 
peripheral blood of monkeys following (□), 500 (•), 750 (a), and 1000 (o) 
rads of gamma rays protracted over 10 days of exposure. Values are the 
averages of surviving animals per group. 



140 



120 



£ 100 



l i r 



i I r 




Gamma-ray exposure 
at 4.1 rads/hr 

I L_ 



J L 



Recovery period 

I I I 



14 18 21 25 28 32 35 
BLEEDING SCHEDULE, days 



39 42 



49 



Fig. 7 Radiation-induced depression and recovery of packed cell volume in 
the peripheral blood, during and following gamma-ray bone-marrow block, of 
two substrains of mice with different radiation-resistance characteristics, o, 
resistant strain; •, nonresistant strain. 



252 



SPALDING AND HOLLAND 



completely dose dependent but is otherwise unknown. The radiation-resistance 
factor given in Fig. 7 has been shown to be genetic and to be consistent with a 
single-gene-locus hypothesis. 

BONE-MARROW RESILIENCE AND "IRREPARABLE INJURY" 

As stated earlier, in successful recovery from radiation injury, the bone 
marrow (hematopoietic tissue) is the organ of primary concern. Thus a 
knowledge of bone-marrow resilience from continuous or repeated radiation 
stress, or both, in the mammal is elementary to an understanding of the 
"irreparable" component of radiation injury and repair kinetics. Protracted or 
fractionated exposures, or both, are required to produce this kind of 
information. Investigations using protracted and fractionated exposures showed 
mouse bone marrow to be extremely resilient to injury from ionizing 




240 320 

TIME, days 



560 



Fig. 8 Peripheral blood characteristics of monkeys 27 and 51 days after 10 
100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were 
given no gamma-ray-insult exposure before the fractionated exposures, a, 
packed cell volume; □, white blood counts; •, lymphocytes; o, neutrophils. 



SPECIES RECOVERY FROM RADIATION INJURY 



253 



radiation. ' Irreparable injury was observed using the method of reduced 
LD50/30 from radiation insult doses after allowing 90 days for repair. 8 The 
resilience of bone marrow and irreparable injury in the mouse have been well 
documented. Monkeys are being investigated to make similar determinations on 
larger mammals. 

Four groups of monkeys were given challenge or insult gamma-ray exposures 
of (control), 500, 750, or 1000 rads protracted over 10 days. They were then 
allowed 14 months to recover from injury inflicted by the insult doses. After the 
recovery period all groups were placed on a gamma-ray-exposure regime that 
subjected them to a 100-rad exposure (at 3 5 rads/hr) every 56 days. 
Bone-marrow resilience and irreparable injury were examined periodically in 
terms of peripheral blood analysis. Figures 8 to 1 1 are graphs of packed cell 
volumes and white blood cell values at 27 and 51 days after each exposure 
during the first 560 days of this gamma-ray-exposure regime. These figures 
illustrate quite clearly the resilience, or recovery capability, of hematopoietic 



60 



^ 50 



1 r 




4 

100 



-a— &- 



Acute dose in rads at 56-day intervals 

* 4 4 4 4 4 4 
100 100 100 100 100 100 100 



4 

100 



4 

100 




240 320 

TIME, days 



560 



Fig. 9 Peripheral blood characteristics of monkeys 27 and 51 days after 10 
100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were 
given an initial 500-rad gamma-ray-insult exposure 14 months before the 
fractionated exposures. ^, packed cell volume; □, white blood counts; •, 
lymphocytes; o neutrophils. 



254 



SPALDING AND HOLLAND 



60 



SS 50 — 



g 40 



30 

16 
14 

^E 12 
E 
i 10 



I 


I I I I I ! I I I I I ! I 


— 


Acute dose in rads at 56-day intervals 


4 

100 


4 4 4 4 4 4 4 4 4 

100 100 100 100 100 100 100 100 100 


— «^^ 


S^y^i 


~ I 


i i i i i i i i i i i i i 



4 — 



80 



160 



240 320 

TIME, days 



400 



480 



560 



Fig. 10 Peripheral blood characteristics of monkeys 27 and 51 days after 10 
100-rad gamma-ray exposures at 56-day intervals. Monkeys in this group were 
given an initial 750-rad gamma-ray -insult exposure 14 months before the 
fractionated exposures. -, packed cell volume; □, white blood counts; •, 
lymphocytes; o, neutrophils. 



tissue in the monkey. It can also be seen from Figs. 8 and 11 that, if an 
irreparable lesion was caused by the 1000-rad insult dose in the third group 
(Fig. 11) or in the other two groups subjected to insult doses (Figs. 9 and 10), it 
is not expressed as a decrement in hematopoietic repair observable in peripheral 
blood. The resilience of the Macaca mulatto, bone marrow to this radiation 
regime is of particular interest because earlier investigations with Macaca 
arctoides, 1 using the fractionation method of exposure but in a more stressful 
regime, showed the monkey to have poor recovery characteristics. 

Almost since the discovery of the injurious effects of ionizing radiation, 
attempts have been made to equate biological injury and recovery to 
mathematical models. Hollister, Vincent, and Cable 1 x pointed to some of the 
frustrations of predicting early radiation lethality over a wide range of exposure 
conditions; however, under a given set of exposure conditions, predictions of 
lethality and irreparable injury have been quite accurate. 12 Thus it seems 



SPECIES RECOVERY FROM RADIATION INJURY 



255 




160 240 320 

TIME, days 



400 



480 



560 



Fig. 11 peripheral blood characteristics of monkeys 27 and 51 days after 10 
100-rad gamma-ray .exposures at 56-day intervals. Monkeys in this group were 
given an initial 1000-rad -gamma-ray-insult exposure 14 months before the 
fractionated exposures. &, packed cell volume; □, white blood counts; •, 
lymphocytes; o, neutrophils. 



inappropriate not to try to predict by use of a simple mathematical model the 
demise of the monkeys involved in this investigation. If we assume that the mean 
repair half-time (RT 50 ) for all body organs, tissues, and related physiological 
functions essential to the sustenance of life is 28 days, that 10% of the 
exposure-dose-related injury is irreversible, and that, when the dose-equivalent 
injury to the whole body reaches 450 rads, 50% lethality can be expected, we 
can make the survival-prediction graph shown in Fig. 12. As shown in the figure, 
the four groups of monkeys in this investigation would theoretically have 
irreparable radiation lesions, which would be expected from acute gamma-ray 
exposures of 0, 50, 75, or 100 rads, or 10% of the insult doses they received 14 
months before the fractionated-gamma-ray-exposure regime. Thus the four 
groups would have effective acute body burdens of 100, 150, 175, or 200 rads 
(Fig. 12) immediately following the first 100-rad gamma-ray fraction. Additional 
100-rad gamma-ray fractions at 56-day intervals would add reparable and 



256 



SPALDING AND HOLLAND 




56 168 280 392 504 616 728 840 952 1064 1176 1288 1400 1512 1624 1736 

TIME, days 

Fig. 12 Graph of an effective-acute-dose (EAD) model to predict the 
accumulation of lethal-dose levels of fractionated gamma rays in monkeys 
with 0-, 500-, 750-, and 1000-rad insult doses 14 months before receiving 10 
100-rad gamma-ray exposures at 56-day intervals. RT 50 is assumed to be 28 
days, and the irreparable component is assumed to be 10%. 



irreparable injury as shown by the line plots for each group, and a lethal body 
burden could be expected following 14 100-rad fractions for the group with a 
1000-rad insult dose and following 22 100-rad exposures in the control group. 
Figures 8 to 11 show that, after 10 100-rad gamma-ray fractions, peripheral 
blood elements in all groups are at physiologically safe levels and hematopoietic 
tissue does not appear degenerate. 

Whether or not animals on this radiation-exposure regime will obligingly 
adjust their physiological state to conform with this model (Fig. 12) cannot now 
be said. One thing is evident, however: Even the monkey, previously rated low in 
terms of recovery capability, has a remarkable tolerance to radiation injur}' when 
exposure and repair conditions are optimum. 

INJURY, RESILIENCE, AND CONTINUITY OF GENETIC MATERIAL 



A discussion of species recovery from radiation injury would be wanting 
without a few words on the possible genetic effects of exposure to ionizing 
radiations. It is commonly known that developing mammalian germ cells are 
among the most radiosensitive cells. Popular genetic theory also propounds that 
the sensitivity of germ cells to the lethal effects of ionizing radiation extends to 
a mutagenic sensitivity that can accumulate significantly and can result in severe 
genetic decrements to future generations. The statement that there is increasing 
evidence of biological effects of small exposures, particularly from a genetic 
standpoint is frequently heard or read. This theory has been perpetuated by 
notable scientific media and by such popular journals as Esquire. 



SPECIES RECOVERY FROM RADIATION INJURY 



257 



Several long-term investigations have been carried out in this and other 
countries to determine the possible genetic hazards of ionizing radiation. In one 
investigation each of 55 generations of male mouse progenitors received acute 
whole-body gamma-ray exposures of 200 rads. A similar experiment in man, 
with a generation time of 30 years, would require 1650 years; thus, for reliable 
data on man, it would have been necessary to start at about the time of the 
Roman Empire. A few comparative characteristics of control and irradiated lines 
of mice which are of possible interest to livestock breeders are shown in Fig. 13. 



1 r 



Total mice weaned 



Litter size weaned: 



Weaning weight' 



Fertile period- 



Life-span of virgin females' 



□ 



□ 



Control Experimental 



Sterility 

Sex ratio, (males/total), 
Birth 52.0 

Weaning 51.5 

Visible mutations 



52.5 
53.5 



(F 



F 55> 



20 40 60 80 100 

% OF CONTROL VALUE 

Fig. 13 Comparative breeding and litter characteristics in control mice and 
mice with up to 55 generations of X-irradiated male progenitors (100 breeding 
pairs per group). 



Experimental animals from 45 generations of irradiated male progenitors had a 
shorter fertile life but weaned larger litters (with slightly smaller weaning 
weights) and produced more total offspring (with longer life spans) than did 
control mice. However, none of these characteristics was significantly different 
from control values. After 5 5 generations, no sterility was observed in either 
line. Sex ratio at birth and weaning did not differ greatly. Only one viable 
mutation was observed — a spontaneous mutation for hairlessness in the control 
line. 

Although this investigation was carried out with intensive inbreeding (which 
in theory is an undesirable scheme to accumulate genetic injury), other 
investigations using different breeding methods have produced similar negative 
findings. Experimental evidence is contrary to the popular theory of radiation- 
induced genetic decrement mentioned previously. Not only is there no increased 
experimental scientific evidence of genetic effects from small exposures but also 



258 SPALDING AND HOLLAND 

experimental results of long-term radiation genetics programs are so disgustingly 
negative that little or no interest can be generated to support such programs. 

ACKNOWLEDGMENT 

This work was performed under the auspices of the U. S. Atomic Energy 
Commission. 



REFERENCES 

1. V. P. Bond, T. M. Fliedner, and J. O. Archambeau, Mammalian Radiation Lethality, A 
Disturbance in Cellular Kinetics, Academic Press, Inc., New York, 1965. 

2. G. W. Casarett, Patterns of Recovery from Large Single-Dose Exposure to Radiation, in 
Comparative Cellular and Species Radio sensitivity , pp. 42—52, Igaku Shoin, Ltd., 
Tokyo, 1969. 

3. N. P. Page, The Effect of Dose-Protraction on Radiation Lethality of Large Animals, in 
The Proceedings of a Symposium on Dose Rate in Mammalian Radiation Biology, D. G. 
Brown, R. G. Cragle, and T. R. Noonan (Eds.), Apr. 29-May 1, 1968, Oak Ridge, 
Tenn., USAEC Report CONF-680410, p. 12.1-23, UT-AEC Agricultural Research 
Laboratory, July 12, 1968. 

4. J. F. Spalding, T. T. Trujillo, and W. L. LeStourgeon, Dependence of Rate of Recovery 
from Acute Gamma-Ray Exposure on Size of the Conditioning Dose, Radiat. Res., 15: 
378-389 (1961). 

5. J. F. Spalding and M. A. Van Dilla, Effect of Size of Dose from Protracted Gamma-Ray 
Exposure on Repair Rate of Hematopoietic Tissue, unpublished. 

6. J. F. Spalding, D. M. Popp, and R. A. Popp, A Within-Strain Difference in Radiation 
Sensitivity in the REM Mouse, Radiat. Res., 40: 37-45 (1969). 

7. J. F. Spalding, D. M. Popp, and R. A. Popp, A Genetic Effect on Radiation Sensitivity 
Consistent with a Single Gene Locus Hypothesis, Radiat. Res., 44: 670-673 (1970). 

8. J. F. Spalding, V. G. Strang, and F. C. V. Worman, Effect of Graded Acute Exposures of 
Gamma Rays or Fission Neutrons on Survival in Subsequent Protracted Gamma-Ray 
Exposures, Radiat. Res., 13: 415-423 (1960). 

9. J. F. Spalding, Comparative Repopulation Recovery of Circulating Erythrocytes 
Following Graded Second Gamma-Ray Exposures in Mice, Radiat. Res., 29: 114—120 
(1966). 

10. J. F. Spalding, L. M. Holland, and O. S. Johnson, Kinetics of Injury and Repair in 
Monkeys and Dogs Exposed to 7-Ray Fractionation, Health Phys., 17: 11 — 17 (1969). 

11. H. Hollister, A. R. Vincent, and J. W. Cable, A Prediction of Early Radiation Lethality 
Using an Effective Dose, USAEC Report CONF-813-1, from the 10th Annual and First 
International Meeting of the Western Section of the Operations Research Society of 
America, September 1964, Honolulu, Hawaii (TAB-R-4). 

12. J. F. Spalding, T. T. Trujillo, and W. L. LeStourgeon, The Predictability of Irreparable 
Biological Damage from Exposure to Ionizing Radiation, Radiat. Res., 15: 754-760 
(1961). 



RADIOIODINE AIR UPTAKE IN DAIRY COWS 
AFTER A NUCLEAR -CRATERING EXPERIMENT 



RONALD E. ENGEL,* STUART C. BLACK,t VICTOR W. RANDECKER,* and 
DELBERTS. BARTH* 

*Bureau of Air Pollution Sciences, Environmental Protection Agency, Research Triangle 
Park, North Carolina, and t Western Environmental Research Laboratory, Environmental 
Protection Agency, Las Vegas, Nevada 



ABSTRACT 

During a nuclear-cratering experiment, four lactating and three dry, pregnant dairy cows 
were exposed to the effluent cloud in an experiment designed to measure the transfer of 
radioiodine to milk, tissues, and excreta of the dairy cow when exposure was due primarily 
to inhalation during cloud passage. 

The lactating cows were milked twice daily. The dry cows were sacrificed at three 
different times after the event. Radioiodine was measured in all milk samples and in 50 
different biological samples from each of the sacrificed animals. The "inhalation" exposure 
as calculated from air-sampler data was not sufficient to account for the observed milk 
levels; this indicated that the majority of the exposure occurred by inadvertent ingestion. 
The term "air uptake" was used to take into consideration all routes of entry. 

At 56 hr postevent the ' 31 I concentration was higher in the abomasal tissue than any 
other tissue except the thyroid and higher in abomasal contents than in the contents of the 
remainder of the gastrointestinal tract. The effective time in abomasal tissue and contents 
was also longer than in other samples, except in the thyroid. In maternal and fetal thyroids, 
the peak concentration occurred at 72 hr postexposure, when the thyroids contained 5.3 
and 4.5%, respectively, of the estimated intake. However, the concentration in fetal thyroid 
was 2 .4 times that of the maternal thyroid. 



Nuclear devices detonated in the atmosphere or in cratering experiments 
produce calculable quantities of radioiodines. However, the concentrations of 
radioiodine observed in the biosphere under different conditions are extremely 
variable. The chemical and physical forms of radioiodines following nuclear 
fission reactions are of major importance. Less is known, quantitatively, about 



259 



260 ENGEL, BLACK, RANDECKER, AND BARTH 

inhalation of radioiodine from field sources than about any other aspect of 
radioactivity resulting from these reactions. 1 

Radioiodines released into the atmosphere and available to the pulmonary 
system may be hazardous only under specific, pertinent conditions existing at 
the time of the release. Biological availability depends on such physical factors as 
the source of the radioiodines, the proximity of the source to the study, and 
meteorological conditions existing before and after release. 

It is difficult to investigate every facet of radioiodine fallout in detail. 
However, adequate exposure and dosage determinations are required for 
establishment of accurate radiation-protection guides. To make these determina- 
tions with regard to inhalation of radioiodines, we must answer the following 
questions: 2 

1. What are the potential sources of atmospheric radioiodine contamination? 

2. What are the chemical and physical properties of both gaseous and 
particulate forms of radioiodines, and what is the degree of fractionation? 

3. What is the particle size distribution inhaled by the animal and the 
biological availability of each size? 

4. What fraction of the intake of radioiodines is retained in the body 
following inhalation? 

5. What are the lung deposition, retention, translocation, and elimination 
factors of inhaled radioiodines in normal physiological states? 

6. What is the distribution of radioiodines in specific tissues and organs of 
various species of animals? 

Nuclear-cratering experiments offer an excellent opportunity to study the 
distribution, deposition, and uptake of radioiodines in dairy cows following 
exposure to the radioactive cloud. This report, the scope of which is limited to 
question 6, deals with the concentrations of 1 3 1 1 in tissues, milk, and excreta of 
dairy cows following exposure to a radioactive cloud produced by the 
4.3 ± 0.4-kt Project Palanquin nuclear-excavation experiment. 

PROCEDURES 

Experimental Design 

Nineteen lactating and three nonlactating, pregnant Holstein cows were 
grouped for this experiment as shown in Table 1. Each animal used was free of 
obvious signs and symptoms of any infectious disease and had no physical 
defects. Assignments to the first four groups were based on a stratified random 
allocation. Lactating cows were first grouped by milk production, butterfat 
production, and days in production and were then randomly assigned to the 
experimental groups. The selection of Group V was based on milk production 
prior to the dry period. 

Groups I, II, and III remained at the dairy barn throughout the entire study 
period. These three groups, which were fed contaminated forage from the three 



RADIOIODINE AIR UPTAKE IN DAIRY COWS 261 



Table 1 
GROUPING OF DAIRY COWS 



Number of 
Group cows Location Type and duration of exposure* 

I 6 Dairy barn Average intake of 8.9 kg/day of 

contaminated green chop from 
Station 3 for 4 days 
II 6 Dairy barn Average intake of 7.1 kg/day of 

contaminated hay from Sta- 
tion 3 for 8 days 

III 3 Dairy barn Average intake of 7.1 kg/day of 

contaminated hay from Station 
2 for 9 days and 9.4 kg/day 
from Station 1 for 12 days 

IV 4 Station 3 Air uptake, exposed during and 

after cloud passage at Station 3 
for 56 hr 
V 3 Station 3 Air uptake, exposed during and 

after cloud passage at Station 3 
for 56 hr 

*The dairy barn was located approximately 70 km from ground zero. Station 1 
was 4.7 km from ground zero at an azimuth of 350° ; Station 2, 5.5 km from ground 
zero at an azimuth of 026° ; and Station 3, 4.6 km from ground zero at an azimuth of 
004°. 



experimental stations, will not be discussed in this report. Groups IV and V, the 
subjects of this report, were maintained at Station 3 from April 6 to 16 and at 
the dairy barn thereafter. 

Station 3 was located 4.60 km from the detonation point at an azimuth of 
4°. The station was located on a terrain that had a slight slope and a moderate 
cover of natural vegetation. Facilities for Station 3 consisted of seven portable 
milking stanchions designed to hold dairy cows comfortably while facing the 
ground zero. 3 Each cow was fitted with a blanket to reduce the exposure to 
cold, wind, and moisture. The stanchions were 0.6 meter apart to allow room for 
the milkers and also to reduce the physical contact between cows. Each 
stanchion had an automatic waterer and removable feed box. Time of milking 
was as close to the regular schedule as possible. Each cow in Group IV was 
milked with the same Surge milking bucket throughout the experiment and with 
the same equipment as normally used at the dairy barn. 4 Milking techniques 
were identical to those used during normal routine milking. Samples of milk, 
grain, water, and hay were taken daily for background determination prior to 
the event. Temperature and respiratory rates were taken for all seven cows in the 
morning and evening. Blood samples for hematology and blood chemistry were 
taken before and after the exposure. Just before the event the feed boxes were 



262 ENGEL, BLACK, RANDECKER, AND BARTH 

removed and the waterers turned off and covered to prevent any further 
ingestion. Because of radiological health procedures, Group IV cows were not 
milked until 31 hr after cloud passage. They were subsequently milked at 40 and 
54 hr postevent. Uncontaminated hay and grain were carried in by the milking 
team. Water was provided only during the milking period. Samples of hay, milk, 
grain, and water were taken at the time of milking. Approximately 56 hr 
postevent all seven animals were returned to the dairy barn, were separated from 
Groups I, II, and III, and were maintained on uncontaminated hay, grain, and 
water. 

Tissue Sampling 

The Group V cows were sacrificed at intervals of 62, 76, and 125 hr after the 
detonation, and a complete and detailed necropsy was done on each animal. 
Milk samples were taken in cubitainers and counted by standard procedures. 5 
Various types of biological samples were taken for gamma-spectrum analysis. 
Samples were put in 400-ml cottage-cheese containers and counted by placing 
the container directly on top of a 10- by 10-cm Nal(Tl) crystal coupled to a 
Technical Measurement Corp. multichannel analyzer. The 200 channels used 
were calibrated at 10 keV per channel (0 to 2 MeV). The spectra were resolved 
by use of the matrix method. Whenever possible, repeat counts were done on all 
available tissues and contents. The minimum detectable activity was approxi- 
mately 100 pCi in the sample for a 20-min counting time. 



RESULTS AND DISCUSSION 

Cow Group Comparisons 

Groups of cows were compared for total serum protein (TP), thyroid binding 
index (TBI), and protein-bound iodine (PBI). The values were not significantly 
different among the groups except for a significantly higher PBI in Group V. The 
hematological values for the cows in the field (Groups IV and V) were not 
essentially different from those for cows in the dairy barn (Groups I, II, and III). 
The variation in milk production of Group IV during the experimental period 
did not differ from that of Groups I, II, and III. Temperature and respiratory 
rates of animals in Groups IV and V did not differ significantly while they were 
at the field station. 

To develop the estimated intake of radioiodines for Groups IV and V, we 
must first assume that there was no physiological difference in any of the 
animals which would affect the metabolism of radioiodine. This assumption is 
justifiable for the following reasons: 

1. On the basis of previous herd history, all groups of cows had equal stable 
iodine intakes throughout the study. 



RADIOIODINE AIR UPTAKE IN DAIRY COWS 263 

2. On the basis of TBI, TP, and milk and butterfat production in the prior 
lactation, Group V cows were not significantly different from the rest of the 
herd. 

3. On the basis of TBI, TP, and temperature and respiratory rates taken 
during the experiment, Group V cows were not essentially different from those 
in other groups except in stage of lactation. 

4. On the basis of the necropsy findings of Group V cows, all cows were 
assumed to be normal and were in good physical condition during the study 
period. 

Air Concentration 

Since instrumentation located at Station 3 indicated that the leading edge of 
the base surge reached the station approximately 12 min after detonation, this is 
the reference time for our calculations. The end time for the calculations is set at 
H + 56 hr, at which time the cows were removed from Station 3. Data from a 
Gelman Instrument Company Tempest air sampler located 30 meters in front of 
the cows were used to determine the integrated air dose for the 56-hr period. 
After the sampler had operated for 30 hr postdetonation, the prefilter and 
charcoal cartridge were changed, and it ran for an additional 24 hr before 
sampling was discontinued. It is reasonable to assume that an insignificant 
exposure occurred during the final 2 hr. The integrated air concentration of i 3 * I 
for the first 30 hr of exposure was 246 jUCi-sec/m 3 (the prefilter was 
190 jiiCi-sec/m 3 and charcoal cartridge was 56 jUCi-sec/m 3 ), and for the next 
24 hr it was 18 jUCi-sec/m 3 . The latter figure indicates that resuspension 
occurred, because the prefilter contained 99.7% of the total activity. 

Exposure Determinations 

The results for the cows exposed by "inhalation" are somewhat different 
from those expected for this type of exposure. The increased concentration in 
the second milking after exposure suggests a delayed absorption of radioiodine 
which is more characteristic of ingestion. 6 This is complicated by the reduced 
milk production of these cows caused by the 31-hr delay between exposure and 
first milking. Cows could have ingested radioiodines by licking the stanchion 
parts or the ground, or the clean feed and water brought to them during the 
reentry period could have been inadvertently contaminated by resuspended 
material. Another indication that inhalation was not the sole source of exposure 
for these cows is the incongruous result obtained by assuming the maximum 
possible inhalation [assuming that (1) the cow breathes at the rate of 100 
liters/min (1.7 X 10" 3 m 3 /sec) (Ref. 7), (2) deposition in the respiratory tract 
was 100%, and (3) the air sampler was 100% efficient] . The cows were exposed 
for 56 hr to integrated air concentrations of 246 juCi-sec/m 3 during the first 
30 hr and 18 /iCi-sec/m 3 for the next 24 hr. The deposition in the cow, with 
these assumptions, would have been: 



264 ENGEL, BLACK, RANDECKER, AND BARTH 

(1.7 X 10" 3 m 3 /sec) (246 MCi-sec/m 3 + 18 ^Ci-sec/m 3 ) = 0.45 juCi (1) 

The average secretion in milk was 25.9 jLlCi, or about 5 7 times this calculated 
intake. 

Since the actual inhalation intake of the seven cows exposed at Station 3 is 
unknown, and since exposure— dose relations are required for the tissue- and 
content-distribution study in the three sacrificed cows, the milk-secretion data 
were used to estimate intake. Because we know that the average secretion of 
Groups II and III (also fed hay and grain) was 10.6%, it is reasonable to estimate 
the total ! 3 1 1 exposure by assuming that cows in Group IV also secreted 10.6% 
of their total radioiodine intake. Therefore the average milk secretion of the 
Group IV cows, 25.9 /iCi, represents 10.6% of their estimated intake of 244 /iCi 
of 131 1. This is reasonable since subsequent field experiments have shown that 
the dairy herd averaged 10.7% 131 I secretion in milk under similar feeding 
regimens using different contaminants. 5,9-13 This average is similar to that 
found by most other investigators. 2 A 4_1 9 

Thus, if our assumptions are correct, it is readily apparent that uptake of 
131 I from inhalation contributed very little [(0.45 X 100)/(244 - 0.45) = 
0.18%] to the total dose. Therefore we use the term "air uptake," which takes 
into consideration inhalation as well as other routes of entry; e.g., skin 
absorption, licking of surroundings, licking of nasal secretions. 

Milk Concentrations 

A peak milk concentration of 1 .6 /xCi/liter for Group IV occurred at the 
second milking. The time of peak was similar to that in controlled studies using 
diatomaceous earth aerosols 5 ' 9 ' 10,12 and in other studies using oral or 
intravenous doses of 131 I (Refs. 15, 16, and 20). The milk data indicate that 
some activity was taken in after the initial exposure. From 40 to 73 hr, the 
effective time (T e ff) was 3 3.1 ± 1.36 hr, and, from 73 to 154 hr, the T e ff was 
16.3 ± 0.9 hr. For both time periods the T e ff was 18.1 ± 0.9 hr. For single- 
exposure studies the milk activity peaks at the first milking and then decreases, 
with a T e ff of less than 24 hr. 

The foregoing results indicate that the l 3 1 1-concentrating mechanisms of 
Group V cows were consistent with those in other studies and that the exposure 
was due to an initial dose followed by continued intake while the cows were at 
the field station. 

Tissue Concentrations from Air Uptake 

An average of 50 biological samples was removed from each of the Group V 
cows and analyzed specifically for 1 3 1 I. The rates of uptake, retention, and 
deposition derived from these data may be useful in developing mathematical 
prediction models and in analog computer simulation. 



RADIOIODINE AIR UPTAKE IN DAIRY COWS 



265 



The data from a different cow at each point in time was used to determine 
the transfer rates between the various body compartments. Effective half-life 
values were determined by assuming that the cows' physiological states were 
equivalent for each point because no lesions of any significance were noted 
during postmortem examination. The half-life (Ty ) was then determined by 
use of the linear-regression line drawn through the three points representing the 
three times of sacrifice. The concentration of I in the biological samples at 
56 hr postevent, the time the animals were removed from further exposure, are 
listed in Table 2. These were calculated by using the Tv to correct for decay 
between removal from Station 3 and sacrifice. 



Table 2 
CONCENTRATION OF ' 3 l I IN BIOLOGICAL SAMPLES 









1 3 ! I sample 




Biological 


Total 




concentration,* 


Retention,tJ 


sample 


weight, g 


Half -life, hr 


MCi/g 


% 


Foregut tissue 


14,600 


34 


205 


1.22 


Foregut contents 


41,350 


34 


760 


12.9 


Abomasum tissue 


2,700 


44 


662 


0.74 


Abomasum contents 


900 


49 


680 


0.6 3 


Hindgut tissue 


7,720 


31 


195 


0.63 


Hindgut contents 


14,000 


31 


680 


3.93 


Maternal thyroid 


37 


230 


345,000 


5.26 


Fetal thyroid 


13 




83 3,000 


4.46 


Liver 


10,000 


29 


91 


0.38 


Respiratory tract 


3,380 


32 


78 


0.11 


Kidney 


1,605 


44 


115 


0.07 


Urine 


309 


20 


880 


0.11 


All others: 










Blood, spleen, 










bone, muscle, skin 


473,330 


34 


16 


3.08 


Total 


570,000 






33.6 



* Activity was corrected to 56 hr postevent. 

t Retention is based on an estimated 244-juCi exposure. 



X Percentage 



sample concentration x total weight 
244juCi 



x 100. 



Certain conclusions are evident based on the T^ in the contents or tissues. 
There were no significant differences for Tu in foregut (rumen, reticulum, and 
omasum), hindgut (duodenum, jejunum, ileum, and colon), respiratory tract, 
and other tissues (blood, spleen, bone, muscle, and skin). The average T^ for 
these compartments, 31.5 ± 2.4 hr, is considered the same as the transport time 
of 1 3 1 1 for nonthyroidal tissues. Lengemann 2 1 observed two half-times for 
various compartments in the dairy cow, a short-lived portion of 17 and 22 hr for 



266 ENGEL, BLACK, RANDECKER, AND BARTH 

blood and feces, respectively, and, later, 58 and 46 hr, respectively, over a 7-day 
period. 

When rats that had inhaled Ag 1 3 1 1 were sacrificed near the time of thyroid 
peak, the gastrointestinal tract, liver, lung, kidney, and spleen were found to 
contain measurable amounts of radioactivity. 22,23 This was considered a 
reflection of the iodine equilibrium beginning to establish itself in the plasma. 
By 50 hr the thyroid contained 60% of the body burden. 

Bustad 24 listed the tissues containing 131 I following establishment of * 3 ! I 
equilibrium in the blood of sheep. The thyroid, feces, mandibular salivary gland, 
milk, abomasal wall, and urine contained concentrations of l 3 1 1 higher than 
those found in the blood. Other tissues (listed in descending order) containing 
concentrations of 1 3 1 1 lower than those in the blood were the parotid gland, 
liver, ovary, kidney, adrenal gland, pituitary gland, lungs, lacrimal gland, heart, 
pancreas, spleen, thymus, brain, and lens. 

Our data clearly show that the Tu of the abomasal tissue (44 hr) is longer 
than that of the other nonthyroidal tissues (32 hr) and shorter than that of the 
thyroid (9.6 days); the thyroid value has been reported to vary between 4.5 days 
for a single oral dose and 16 days for a single contaminating event. 6 Assuming an 
uptake of 244 jiiCi of ! 3 1 1, 3 3.6% of the total estimated exposure was found in 
the tissues by the methods used in this study. The remainder of the 1 3 ! I is 
assumed to have been eliminated via feces and urine; this assumption is 
consistent with data reported by others 15 ' 17,21 and tends to confirm the 
calculated uptake. 

The high percentage of iodine recovered from the intestinal contents 
indicates uptake by ingestion, but it may have been due partly to elimination of 
a large percentage of the deposited particulate matter from the lung via the 
"mucous— cilia escalator"; i.e., the material was coughed up, swallowed, and 
absorbed via the gastroenteric route. It has been suggested that the gastro- 
intestinal tract can be an important route of entry of inhaled material into the 
systemic circulation. 25 The T^ of 9.6 days for the thyroid also indicates a 
continued uptake rather than a single-dose type of exposure. 

Barua, Cragle, and Miller 26 reported that, by using a nonabsorbed 
marker-technique ( 144 Ce), they were able to determine the net absorption of 
orally administered radioiodine in young animals. The rumen appeared to be a 
major site of absorption, and the abomasum a major site of endogenous 
secretion. Net absorption occurred from the second section of the small intestine 
throughout the remainder of the tract. When sodium iodide was administered 
intravenously \ hour before slaughter, a significantly greater concentration of 
radioactivity was found in the abomasum than in the first part of the small 
intestine. 

Our data tend to substantiate these findings. Our data indicate that, on an 
activity per weight basis, at 56 hr the foregut and hindgut tissue were 
approximately equal, each having about one-third the concentration of the 
abomasum. The concentration of 131 \ in the contents of each was also similar, 



RADIOIODINE AIR UPTAKE IN DAIRY COWS 267 

about one-half that of the abomasum contents. It appeared that net absorption 
of iodine was taking place throughout the tract at the same rate as was the net 
loss, i.e., that secretion was equal to absorption. This suggests that, as shown by 
others, 27 a constant physical relation, or equilibrium, exists in the lower tract 
for iodine. 

The percent of calculated intake in the thyroid of the adult and the fetus 
was in close agreement with that found in the literature. 28 ' 29 Concentrations of 
1 3 1 1 in the fetal thyroid during advanced gestation may be one to two times 
that in the adult thyroid of sows, two to three times that in the thyroid of ewes, 
and up to six times that in the thyroid of cows. In this experiment the fetal 
thyroid concentration was 2.4 times that of the maternal cow. 

Swanson, Lengemann, and Monroe 30 found a rapid concentration of J 3 i I in 
the thyroid in the first two days with a slower increase to the peak uptake on 
the third day. The winter peak of 18.4% uptake was reached on the third day, 
but the summer peak of 18.0% was not reached until the fifth day. The 
estimated peak for our studies is at 72 hr, which is similar to the winter peak and 
at a concentration of 5.2% of the estimated dose. Garner et al. 1 reported a 
peak uptake of 5% at 48 hr and an effective half-life of 4.5 days in dairy cows. 

REFERENCES 

1. H. D. Bruner, Symposium on the Biology of Radioiodine: Statement of the Problem, 
Health Phys., 9. 1083 (1963). 

2. R. E. Engel, Potential Hazards as a Result of Inhalation of Radioiodines: A Literature 
Survey, USAEC Report TID-22693, Southwestern Radiological Health Laboratory, 
Jan. 5, 1966. 

3. Southwestern Radiological Health Laboratory, Radioiodine Study in Conjunction with 
Project Sulky, USAEC Report SWRHL-29-r, May 27, 1966. 

4. Southwestern Radiological Health Laboratory, ' 3 ' I Dairy Cow Uptake Studies Using a 
Gaseous Aerosol, SWRHL, preliminary data, 1968. 

5. D. S. Barth and M. S. Seal, Radioiodine Transport for a Synthetic Dry Aerosol Through 
the Ecosystem Air-Forage— Cow— Milk Using a Synthetic Dry Aerosol, in Radio- 
ecological Concentration Processes. Proceedings of the International Symposium, 
B. Aberg and F. P. Hungate (Eds.), Pergamon Press, Inc., New York, 1966. 

6. L. K. Bustad, D. H. Wood, E. E. Elefson, H. A. Ragan, and R. O. McClellan, 1-131 in 
Milk and Thyroid of Dairy Cattle Following a Single Contamination Event and 
Prolonged Daily Administration, Health Phys., 9: 1231 (1963). 

7. National Academy of Sciences, Handbook of Respiration, W. B. Saunders Company, 
Philadelphia, 1958. 

8. S. C. Black, R. E. Engel, V. W. Randecker, and D. S. Barth, Radioiodine Studies in Dairy 
Cows Following the Palanquin Event, USAEC Report PNE-914F, Southwestern 
Radiological Health Laboratory, 1971. 

9. R. E. Stanley, S. C. Black, and D. S. Barth, ' 3 ! I Dairy Cow Studies Using a Dry 
Aerosol, USAEC Report SWRHL-42-r, Southwestern Radiological Health Laboratory, 
August 1969. 

10. Southwestern Radiological Health Laboratory, ' 3 ' I Dairy Cow Uptake Studies Using a 
Submicron Synthetic Dry Aerosol (Project SIP), USAEC Report SWRHL-39-r, April 
1971. 



268 ENGEL, BLACK, RANDECKER, AND BARTH 

11. Southwestern Radiological Health Laboratory, 131 l Transport Through the Air- 
Forage— Cow— Milk System Using an Aerosol Mist (Project Rainout), Report 
SWRHL-43-r, 1967. 

12. S. C. Black, D. S. Barth, R. E. Engel, and K. H. Falter, Radioiodine Studies Following 
the Transient Nuclear Test (TNT) of a KIWI Reactor, USAEC Report SWRHL-26-r, 
Southwestern Radiological Health Laboratory, May 1969. 

13. W. Shimoda, S. C. Black, K. H. Falter, R. E. Engel, and D. S. Barth, Study of a 
Single Dose 131 i- 126 I Ratio in Dairy Cows, USAEC Report SWRHL-27-r, South- 
western Radiological Health Laboratory, April 1970. 

14. R. J. Garner, B. F. Samson, and H. G. Jones, Fission Products and the Dairy 
Cow. III. Transfer of l3 ' I to Milk Following Single and Daily Dosing, J. Agr. Sex., 55: 
283 (1960). 

15. R. J. Garner and H. G. Jones, Fission Products and the Dairy Cow. IV. The Metabolism 
of 131 I Following Single and Multiple Doses, J. Agr. Sci., 55: 387 (1960). 

16. R. F. Glascock, The Secretion of a Single Tracer Dose of Iodine (Labeled) in the Milk of 
the LactatingCow,J. Dairy Res., 21: 316 (1954). 

17. F. W. Lengemann and E. V. Swanson, A Study of the Secretion of Iodine in Milk of 
Dairy Cows Using Daily Oral Doses of 131 I, J. Dairy Set., 40: 216 (1957). 

18. L. B. Sasser and C. A. Hawley, Jr., Secretion of 1 3 ' I into Milk Under Conditions of 
Environmental Contamination of Pasture, J. Dairy Sci., 49: 1501 (1966). 

19. H. M. Squire, L. J. Middleston, B. F. Samsom, and C. R. Coild, Experiments on the 
Metabolism of Certain Fission Products in Dairy Cows, in Radioisotopes in Scientific 
Research, Proceedings of the International Conference, Paris, September 1957, R. C. 
Extermann (Ed.), Vol. 4, Pergamon Press, Inc., New York, 1958. 

20. K. Steenberg, Secretion of I 131 from a Dairy Cow After an Oral Administration of a 
Single Dose in Aqueous Solution, Acta Agr. Scand., 9: 198 (1959). 

21. F. W. Lengemann, 1 3 ' 1 Concentrations in Blood, Milk, Urine, and Feces of Dairy Cows 
Following a Single Dose of Radioiodine, J. Agr. Sci, 61: 375 (1963). 

22. W. J. Bair, Deposition, Retention, Translocation, and Excretion of Radioactive Particles, 
in Inhaled Particles and Vapours, C. N. Davies (Ed.), Pergamon Press, Inc., New York, 
1961. 

23. D. H. Willard and W. J. Bair, Behavior of 1-131 Following Its Inhalation as a Vapor and 
as a Particle, Acta. Radiol., 55: 486 (1961). 

24. L. K. Bustad, Metabolism of 131 I in Sheep and Swine, USAEC Report HW-SA-2267, 
General Electric Company, 1961. 

25. National Academy of Sciences, Effects of Inhaled Radioactive Particles, Report of the 
Subcommittee on Inhalation Hazards, Publication 848, Washington, D. C, 1961. 

26. J. Barua, R. G. Cragle, and J. K. Miller, Sites of Gastrointestinal-Blood Passage of Iodide 
and Thyroxine in Young Cattle, J. Dairy Sci., 47: 539 (1964). 

27. R. G. Cragle, J. K. Miller, and P. T. Chandler, Gastro-Intestinal Sites of Absorption and 
Secretion of Ca, P, Zn, and I in Dairy Cattle, in Radioisotopes in Animal Nutrition and 
Physiology, Symposium Proceedings, Prague, 1964, International Atomic Energy 
Agency, Vienna, 1965 (STI/PUB/90). 

28. J. K. Miller, E. W. Swanson, P. W. Aschbacher, and R. G. Cragle, Iodine Transfer and 
Concentration in the Prepartum Cow, Fetus, and Neonatal Calf, J. Dairy Sci., 50: 1301 
(1967). 

29. National Academy of Sciences, Damage to Livestock from Radioactive Fallout in Event 
of Nuclear War, Report by the Subcommittee on Livestock Damage, Publication 1078, 
Washington, D. C, 1963. 

30. E. W. Swanson, F. W. Lengemann, and R. A. Monroe, Factors Affecting the Thyroid 
Uptake of 131 I in Dairy Cows, J. Anim. Sci., 16: 318 (1957). 



PROBLEMS IN POSTATTACK 
LIVESTOCK SALVAGE 



S. A. GRIFFIN* and G. R. EISELE 

Oak Ridge National Laboratory, Oak Ridge, Tennessee, and 

UT— AEC Agricultural Research Laboratory, Oak Ridge, Tennessee 



ABSTRACT 

Studies were initiated in 1968 to determine whether the meat from irradiated animals could 
be utilized safely by humans in a nuclear disaster. Pigs weighing approximately 200 to 
250 1b were exposed to 700 R (air dose) of whole-body gamma irradiation at 1 R/min. 
Blood samples were taken before and after irradiation to detect bacteremia. No evidence of 
bacteremia was found in any of the pigs. Various bacteria were isolated from the lymph and 
liver. In some animals bacteria were isolated from the muscles. No difference in the 
incidence of bacterial invasion was found between irradiated and control animals. 

Not being able to detect bacteremia in pigs, we conducted a pilot study on rats to verify 
previous work and to evaluate our techniques. Rats exposed to 800, 900, and 1000 R of 
whole-body gamma irradiation at 50 R/min developed bacteremia, the severity and 
incidence increasing with the increase in total dose. 

A problem of major concern in a postattack situation is that of maximum 
utilization of available livestock for human food. At present the general 
recommendations are that animals exposed to radiation can be used for food 
before they show radiation sickness and after they have recovered (National 
Academy of Sciences— National Research Council, 1963). However, this proce- 
dure may not be feasible under postattack conditions. The literature indicates 
that animals exposed to a lethal dose of whole-body irradiation may develop 
bacteremia (bacterial invasion into the circulatory system). However, most of 
the experimental work has been done with laboratory animals. 

Hammond, Anderle, and Miller 1 exposed mice (10-week-old CF-1 females) 
to three levels of continuous gamma radiation from a 60 Co source. The animals 



*Present address: Dean of Agriculture, Tennessee Technological University, Cookeville, 
Tenn. 



269 



270 GRIFFIN AND EISELE 

were then challenged by intraperitoneal injection of Pseudomonas aeruginosa. 
These authors concluded that increased susceptibility to this infection was 
related to rate of irradiation rather than to the total accumulated dose. 

Silverman et al., using mice exposed to supralethal doses of neutron or 
combined neutron and gamma radiation from a nuclear device, reported that 
mice with a short survival time had a larger percentage of positive spleen cultures 
than of positive heart blood cultures. Similar results were also reported by 
Gonshery, Marston, and Smith. 3 Silverman et al. also concluded that the ability 
of the spleen to remove bacteria may not be impaired but that it may be unable 
to destroy the increased number of bacteria and thus bacteremia eventually 
develops. 

Miller, Hammond, and Tompkins exposed male mice weighing approxi- 
mately 20 g to 450 or 600 R of total-body X irradiation. The majority of the 
animals had bacteremia severe enough to be considered an overwhelming sepsis, 
which was to a large degree responsible for their deaths. 

Kossakowski, 5 working with rabbits exposed to doses of 1000 and 1200 R 
of X rays, reported no bacteremia during the course of acute radiation sickness. 
However, the muscles and internal organs showed an increase in bacteria 
isolated. He concluded that positive results from bacteriological investigation of 
blood cannot be regarded as an indication of postradiation autoinfection. 

Warren and Whipple 6 obtained negative blood cultures from dogs exposed to 
a lethal dose of X ray. Lawrence and Tennant 7 reported that mice exposed to 
1000 R of X rays (LD 50 = 550 to 600 R) or equivalent doses of neutrons were 
bacteriologically clean when killed 1, 2, 3, or 4 days after irradiation. When 
killed 5 to 1 1 days postirradiation, mice receiving 700 to 800 R did show 
positive blood cultures. 

Pawel, Kalousova, and Vranovska 8 reported on bacterial evaluation of meat 
of slaughtered swine that had received a total dose of 700 R at 100 R/3 3 min. 
They concluded: 

1. A penetration of germs outside the intestinal tract occurs already in the 
period of the disease in which the manifest clinical symptoms of acute 
irradiation sickness are not yet developed. 2. Germs are found first of all in 
the organs, i.e., particularly in the liver and in the spleen. 3. Among the 
germs found in irradiated animals we diagnosed no representatives of the 
principal infectious diseases of pigs caused by bacteria. The majority of the 
micro-organisms found consisted of coliform germs and streptococci. 

In a short-term experiment, Wasserman and Trum 9 reported that the flesh 
from lethally irradiated animals (cows and sheep) was not detrimental when 
ingested by dogs. These authors also reported similar results when meat and/or 
selected organs were fed to albino rats and chickens. 1 ° 

Studies were initiated in 1968 at Oak Ridge to determine whether the meat 
from lethally irradiated animals could safely be used for human consumption in 
a nuclear disaster. Our initial objective was to determine whether farm animals 



POSTATTACK LIVESTOCK SALVAGE 271 

developed bacteremia and if there was further invasion of the organs and 
muscles. 



EXPERIMENTAL PROCEDURE 

The 60 Co variable-dose-rate irradiation facility at UT— AEC Agricultural 
Research Laboratory was used as the radiation source in these studies. A total 
bilateral exposure dose of 700 R (air dose) at 1 R/min was used. It was 
estimated that this level of irradiation would approach an LD 80 /3o- 

All animals were examined by a veterinarian for any abnormalities or disease 
prior to irradiation. Complete hematological studies were done before irradiation 
and at various time intervals after irradiation, especially at the time animals 
showed visual symptoms of radiation sickness. 

Pigs 

The procedures for the collection of blood samples, for necropsy, and for 
microbiological evaluations were the same as those reported by Eisele and 
Griffin. 1 l Visual observation was the major method used to determine when the 
animal was suffering from severe radiation sickness. The following criteria were 
used: 

1. Passage of small amounts of blood in the stool. 

2. Slight but continuous discharge of blood from the snout. 

3. Impairment of weight gain. 

4. Apathy. 

5. Muscular weakness and/or excitability. 

Fifteen Duroc pigs averaging 200 to 250 1b were exposed to 700 R at 
1 R/min and were sacrificed 10 days later under commercial slaughter con- 
ditions. Bacteriological studies were carried out on the blood, muscle, liver, 
and lymph nodes at the time of slaughter. Further bacterial examination was 
done on the muscle after the carcasses had hung in a cooler for 5 days at 38°F. 
For chemical analysis at a later date, muscle samples were taken at slaughter and 
after 5 days in the cooler. These samples were vacuum packed and frozen. The 
hams from these animals were dry cured and smoked. 

Rats 

Adult female rats 1 to 2 years old and weighing approximately 300 g were 
exposed to 800, 900, and 1000 R of whole-body gamma irradiation at 
50 R/min. Five controls, 10 irradiated controls, and 15 irradiated and bled rats 
were used for each level of irradiation. Blood samples were taken via cardiac 
puncture when the rats showed symptoms of radiation sickness or were in a 
moribund state. 



272 GRIFFIN AND EISELE 

RESULTS AND DISCUSSION 

Pigs 

The gross pathological findings at slaughter were multiple ecchymotic and/or 
petechial hemorrhages in the lungs and throughout the wall and mucosa of the 
intestines, petechial hemorrhages in the ventral abdominal region, ecchymotic 
hemorrhages in the stomach (pylorus and/or fundus), and enlarged lymph nodes 
with peripheral congestion. These findings were quite similar to those in earlier 

Pigs- 
Bacteria were isolated from lymph nodes, liver, and muscle (Tables 1 and 2). 
There were no differences in the percentage of positive samples between the 
irradiated and control groups. At 5 days postslaughter the carcasses were 
examined for additional bacterial study. Twenty percent of the samples 
indicated some type of bacterial growth, but these were not the same carcasses 
that showed bacterial growth at the time of slaughter. 

Table 1 

BACTERIA ISOLATED FROM 11 SWINE 
EXPOSED TO 700 R AT 1 R/MIN* 

Number of positive 
Tissue cultures Positive cultures, % 

Lymph 10 91 

Liver 3 27 
Muscle (sampled at 

slaughter) 1 9 
Muscle (5 days 

postslaughter) 2 18 

* All blood samples were negative. 

Table 2 
BACTERIA ISOLATED FROM 4 CONTROL SWINE* 



Tissue 

Lymph 

Liver 

Muscle (sampled at 

slaughter) 
Muscle (5 days 

postslaughter) 



Number of positive 




cultures 


Positive cultures, 


4 


100 


1 


25 


2 


50 


1 


25 



* All blood samples were negative. 



POSTATTACK LIVESTOCK SALVAGE 273 

Since in the previous trials 1 several methods of slaughtering and meat 
handling were evaluated, the only comparison we can make with these trials is in 
the incidence of bacteria in the muscle. These comparisons indicate that the 
meat in the earlier trials was probably contaminated in the handling and 
preservation, whereas the pigs in this experiment were slaughtered under sanitary 
conditions and showed virtually no bacterial activity. Thus, in a postattack 
situation where slaughtering facilities are usable, the degree of microbial activity 
will be at a minimum provided the meat can also be properly handled and 
stored. On the other hand, regardless of the slaughtering procedure practiced, if 
the meat is not properly stored, a buildup of bacteria will occur. 

Two hams were cooked to an internal temperature of 180 C and randomly 
sampled to see if any organoleptic differences could be noticed. All individuals 
participating in the sampling were informed that one ham was taken from an 
animal exposed to a lethal dose of gamma radiation and the other ham was a 
control. The following results were obtained: 

Preference Number 

Irradiated ham 46 

Control ham 43 

Undecided 3 

Total number of participants 92 



Rats 

Inasmuch as we did not observe bacteremia in the pigs, a pilot study was 
conducted to test our techniques with rats, since the literature indicated that 
bacteremia did occur in laboratory animals exposed to lethal radiation. 

Bacteremia was noted in all groups, the severity and incidence increasing 
with the increase in total dose (Table 3). This difference in the incidence of 
bacteremia between the rats and the pigs may be due in part to the different 
dose rates. 

Steers 

Bacteriological studies were also carried out on steers receiving various types 
of radiation insults as a part of the study by Bell, Sasser, and West. 1 Blood 
samples were taken from nine animals that had received various insults 
approximately 8 months earlier. All samples were negative. 

Bacteriological evaluations were carried out on the liver, lymph, muscle, and 
spleen of four animals at the time they were sacrificed (Table 4). All these 
animals had received skin irradiation and had large open sores on the skin. One 
animal had received a gastrointestinal insult in addition to the skin irradiation, 
and the damage to the rumen had healed. 



274 



GRIFFIN AND EISELE 



Table 3 

BACTERIA ISOLATED FROM 15 RATS RECEIVING 
DOSES AT 50 R/MIN* 





Number of 








positive 


Positive 


Summary of organisms 


Group 


cultures 


cultures, % 


isolated 


1000 R 


9 


82 


Escherichia coli 
Pseudomonas species 
Proteus species 
Bacillus subtilis 
Beta-hemolytic 
Streptococcus 


900 R 


10 


75 


Escherichia coli 
Aerobacter aerogenes 
Bacillus subtilis 
Beta-hemolytic 

Streptococcus 
Gamma-hemolytic 

Streptococcus 


800 R 


9 


60 


Escherichia coli 
Aerobacter aerogenes 
Proteus species 
Beta-hemolytic 

Streptococcus 
Staphylococcus 

aureus 



All control rats had negative blood cultures. 



CONCLUSIONS 

From these studies it appears that bacteremia was not present in the swine; 
this indicates that the reticuloendothelial system was not impaired to such an 
extent that bacterial invasion occurred. The low incidence of positive cultures of 
the liver also suggests that a bacteremia did not occur. 

Additional trials with pigs will be carried out at a dose rate of 45 R/min, and 
steers will be studied at the 1- and 45-R/min dose rates. These animals are now 
available, and the experiments will be completed this year. 



ACKNOWLEDGMENTS 



Oak Ridge National Laboratory is operated by Union Carbide Corporation 
for the U. S. Atomic Energy Commission. 



POSTATTACK LIVESTOCK SALVAGE 



275 



Table 4 

BACTERIOLOGICAL FINDINGS FROM STEERS 
EXPOSED TO RADIATION INSULTS 



Steer 


Type of 


Time of 


Tissue 


Bacteriological 


number 


irradiation 


evaluation 


sample 


findings 


138 


Skin 


9 months 


Muscle 


Negative 






after 


Spleen 


Negative 






irradiation 


Liver 
Lymph 


Escherichia coli 
Bacillus subtilis 
Staphylococcus albus 
Beta-hemolytic Streptococcus 
Staphylococcus albus 
Pseudomonas species 


135 


Skin 


10 months 


Muscle 


Negative 






after 


Spleen 


Negative 






irradiation 


Liver 
Lymph 


Beta-hemolytic Streptococcus 
Bacillus subtilis 
Sarcina species 
Staphylococcus albus 
Beta-hemolytic Streptococcus 
Nonhemolytic Streptococcus 


151 


Skin and 


9 months 


Muscle 


Negative 




whole b6dy 


after 


Spleen 


Negative 






irradiation 


Liver 
Lymph 


Pseudomonas species 
Staphylococcus albus 
Negative 


152 


Skin and 


10 months 


Muscle 


Negative 




gastrointestinal 


after 


Spleen 


Negative 






irradiation 


Liver 

Lymph 


Beta-hemolytic Streptococcus 
Escherichia coli 
Aerobacter aerogenes 
Staphylococcus albus 



The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U.S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was sponsored by the U. S. Atomic Energy Commission and is 
published with the permission of the Dean of the University of Tennessee 
Agricultural Experiment Station, Knoxville. 



REFERENCES 

l.C. W. Hammond, S. K. Anderle, and C. P. Miller, Effect of Continuous Gamma 
Irradiation of Mice on Their Leukocyte Counts and Susceptibility to Bacterial Infection, 
Radiat. Res., 11: 242-252 (1959). 



276 GRIFFIN AND EISELE 

2. M. S. Silverman, V. P. Bonx, V. Greenman, and P. H. Chin, Bacteriological Studies on 
Mice Exposed to Supralethal Doses of Ionizing Radiations. I. Radiation from a Nuclear 
Device, Radiat. Res., 7: 270-276 (1957). 

3. L. Gonshery, R. Q. Marston, and W. W. Smith, Naturally Occurring Infections in 
Untreated and Streptomycin-Treated X-Irradiated Mice, Amer. J. Physiol., 172: 
359-364(1953). 

4. C. P. Miller, C. W. Hammond, and M. Tompkins, The Role of Infection in Radiation 
Injury,./. Lab. Clin. Med., 38: 331-343 (1951). 

5. S. Kossakovvski, The Investigations on the Possibility of Vital Diagnosis of Post-Radia- 
tion Autoinfection in Slaughter Animals, Med. Wet. (Poland), 24: 449—45 3 (1968). (In 
Polish) Nuclear Science Abstracts, 24: 877, Jan. 15, 1970. 

6. S. L. Warren and G. H. Whipple, Roentgen Ray Intoxication. I. Bacterial Invasion of the 
Blood Stream as Influenced by X-Ray Destruction of the Mucosal Epithelium of the 
Small Intestine, J. Exp. Med., 38: 713-721 (1923). 

7. J. H. Lawrence and R. Tennant, The Comparative Effects of Neutrons and X-Rays on 
the Whole Body, J. Exp. Med., 66: 667 (1937). 

8. O. Pawel, V. Kalousova, and J. Vranovska, Results Obtained in Microbiological Tests of 
Meat and Slaughtered Swine Afflicted by Radiation Sickness, Vet. Med. (Prague), 12: 
361-366 (1967). 

9. R. H. Wasserman and B. F. Trum, Effect of Feeding Dogs the Flesh of Lethally 
Irradiated Cows and Sheep, Science, 121: 894-896 (1955). 

10. B. F. Trum and R. H. Wasserman, Progress Report to the Office of the Surgeon General, 
U. S. Army, September 1954. 

11. G. Eisele and S. A. Griffin, Problems of Livestock Salvage, in Annual Progress Report, 
Civil Defense Research Project. March 1968-March 1969, USAEC Report ORNL-4413, 
Part 1, pp. 97-100, Oak Ridge National Laboratory, October 1969. 

12. G. Eisele and S. A. Griffin, Problems of Livestock Salvage, in Civil Defense Research 
Project Annual Progress Report. March 1969-March 1970, USAEC Report ORNL- 
4566(Pt. 1), Oak Ridge National Laboratory. 

13. M. C. Bell, L. B. Sasser and J. L. West, Simulated-Fallout-Radiation Effects on 
Livestock, this volume. 



EXPOSURE-RATE EFFECTS ON SOYBEAN PLANT 
RESPONSES TO GAMMA IRRADIATION 



M. J. CONSTANTIN, D. D. KILLION, and E. G. SIEMER* 

UT— AEC Agricultural Research Laboratory, Oak Ridge, Tennessee 



ABSTRACT 

Seedlings of Glycine max (L.) Merrill were gamma irradiated at either 2 to 3 or 12 days 
postemergence and scored for seedling growth reduction at either 25 to 30 days 
postemergence or for stem length at various times through maturity and yield. The results 
showed an exposure-rate effect the extent of which was dependent on exposure, stage of 
development when irradiated, and/or the end point scored. Seedling responses showed a rate 
saturation at 50 R/min, whereas the mature-plant responses showed a rate saturation at 
2 5 R/min. Shoot dry weight was decreased to 50% of control by 3 kR at 50 R/min and by 5 
kR at 10 R/min. Yield was reduced to approximately 50% of control by 2.5 kR at from 
6.25 to 50 R/min. At 5.0 kR, yield was approximately 20% of control at 6.25 R/min, 10% 
at 12.5 R/min, and essentially zero at 25 and 50 R/min. Results of a split-exposure 
experiment demonstrated repair, which occurred within a radiation-free period of 30 to 
120 min at an exposure of 4 kR. Decreasing the exposure rate from 36.4 to 20 R/min 
permitted a greater degree of repair to occur in the plants than occurred during a split 
exposure of 4 kR at 50 R/min with a radiation-free period of 120 min. 



Sparsely ionizing radiation delivered at low rates is less effective in living systems 
than radiation at high rates; i.e., there is a dose-rate effect. Evidently the 
magnitude of dose-rate effects in living organisms depends partly on dose of 
ionizing radiation 1 ,2 and on end point scored. 1 The extent of radiation-induced 
damage observed in an organism is the sum of direct and indirect effects minus 
repair and recovery that may occur during as well as after irradiation. It has been 
shown that repair processes are responsible for the extent of dose-rate effects in 
living systems (see reviews by Casarett 3 and Sacher 4 ). Dose-rate effects have been 



*Present address: Mountain Meadow Research Laboratory, Colorado State University, 
Gunnison, Colo. 

277 



278 CONSTANTIN, KILLION, AND SIEMER 

investigated more extensively in mammalian than in botanical systems. (For 
recent compilation of pertinent data, see the Proceedings of a Conference on 
Dose Rate in Mammalian Radiation Biology, Apr. 29— May 1, 1968, Oak Ridge, 
Tenn., USAEC Report CONF-680410, UT-AEC Agricultural Research Labora- 
tory, 1968.) There is, however, ample evidence in the literature that dose-rate 
effects occur in botanical systems. 2 ' 5_1 

The extensive research data of Sparrow et al. 10 demonstrate the extent of 
differential response to ionizing radiation among species of plants and among 
developmental stages of the life cycle within species as influenced by exposure 
procedures and environmental conditions. Our research with plants of major 
food crops, which is of a civil-defense nature, has provided results that concur 
with this statement. Most of the work, however, was done at an exposure rate of 
50 R/min, which is considerably higher than that expected in areas of 
radioactive fallout. Currently emphasis is being placed on studies involving 
exposure and exposure rates at different plant developmental stages in a number 
of species. 

In this report of progress, we present data on the response of soybean plants 
[Glycine wax (L.) Merrill] to varying gamma-ray exposures as influenced by 
exposure rate. Results of split-exposure experiments are presented as evidence of 
repair processes that occur in the soybean plant and as one explanation for the 
exposure-rate effect observed. 



MATERIALS AND METHODS 

The experiments were conducted in two phases, one involving seedling 
growth of the variety Hill under environment-controlled conditions and the 
other involving plant growth and yield of the variety Kent under outdoor 
conditions. Plants in both cases w T ere grown in a Perlite : soil : peat : sand me- 
dium (3:2:1:1 by volume) with the pH adjusted to approximately 6.5 and 
with nutrients added. The 60 Co variable-dose-rate facility of the UT— AEC Agri- 
cultural Research Laboratory was used for all experiments. 

In the seedling, experiments four seeds were planted in each 6-in. pot, and 
the plants were thinned to two per pot at the time of irradiation. Plants were 
irradiated on day 2 or 3 postemergence, at which time the primary (unifoliolate) 
leaves were unfolding. Plants were removed from the environment-controlled 
room, taken to the °Co source, irradiated, and then returned to the 
environment-controlled room (83 ± 2 F, 16 hr of light daily, and 50 ± 10% 
relative humidity). The different exposures and exposure rates caused the 
duration of irradiation to vary; therefore plants of all treatments were subjected 
to equal periods of time in the source building at a light intensity and 
temperature regime les. than that in the environment-controlled room. Sham 
controls were grown for each experiment. In the split-exposure experiment, light 
intensity and temperature in the source building were equal to those in the 



EXPOSURE-RATE EFFECTS 279 

environment-controlled room. Plants were harvested at 25 to 30 days postirra- 
diation, and data presented are oven-dried weights of the shoot above the 
unifoliolate leaves. Axillary shoot growth is not included. 

In the outdoor experiments four plants were grown per 5 5-gal drum, which 
was cut in half crosswise. The plants were irradiated at 12 days after emergence; 
exposures were 2.5 and 5.0 kR at either 6.25, 12.5, 25, or 50 R/min. The 
criteria of evaluation for plant response to gamma rays were stem length at 
varying times postirradiation and yield. Late planting caused the plants to be 
subjected to a killing frost prior to complete maturity; therefore, "yield" refers 
to the oven-dried weight of pods and immature beans. "Stem length" refers to 
the distance between the tip of the shoot apex and "ground" level. 

RESULTS 

A preliminary experiment (data not shown) with seedlings of Hill soyabeans 
exposed to gamma rays at 5, 50, and 500 R/min indicated little or no 
exposure-rate effect at 2 kR, and at 4 kR the response became independent of 
rate (the point at which response becomes independent of rate is hereafter 
referred to as exposure-rate saturation) at 50 R/min. A number of experiments 
have been conducted since then with exposure rate being one of the variables. 
Results in Fig. 1 show that shoot weight of soybean seedlings exposed to 4 kR at 
rates of from 3.125 to 400 R/min reached a rate saturation at approximately 
50 R/min. 



100 



o 

oc 60 



O 40 



20 



III 1 


1 


1 




1 


- 


\ 






4 kR 




- 


-\ 


V- 


—4- 






1 1 


II 1 1 


1 


1 






1 



\ 25 50 100 200 400 

^A> EXPOSURE RATE, R/min 

Fig. 1 Shoot dry weight of Hill soybean seedlings as influenced by 4 kR of 
Co gamma radiation administered at exposure rates of 3.125 to 400 R/min. 



280 



CONSTANTIN, KILLION, AND SIEMER 



The results of another experiment (Fig. 2) show the relation that exists 
between exposure and exposure rate for soybean seedling response to gamma 
rays. Shoot dry weight was reduced to 50% of control (unirradiated) by either 3 
or 5 kR, depending on whether the rate was 50 or 10 R/min, respectively. The 
magnitude of the interaction of exposure and exposure rate can be demonstrated 
by the ratio of shoot dry weight expressed as percent of control for the 
10 R/min vs. the 50 R/min population. The ratios were 1.1, 6.8, 7.0, and 3.6 at 
2, 4, 6, and 8 kR, respectively. 



100 



60 



40 



20 



— 


i> 


I 




I 


— 


— 






\ 10 R min 




— 


— 


i 


\ 50 R mm 






— 




I 








•X 



EXPOSURE, kR 

Fig. 2 Influence of exposure on the magnitude of exposure-rate effect 
demonstrated by shoot dry weight of Hill soybean seedlings following Co 
gamma irradiation. 



An outdoor experiment with Kent soybeans was scored for (1) increase in 
stem length vs. time after irradiation, (2) stem length at maturity, and (3) yield. 
Results for indexes 1 and 2 are shown in Fig. 3. The seedlings were irradiated at 
on the abscissa, which was 12 days postemergence (early log phase of growth). 
The plants ceased to increase in stem length at various times after irradiation; 
this response was dependent on exposure and exposure rate. At 2.5 kR stem 
length ceased to increase after 20 to 25 days postirradiation regardless of the 
exposure rate used. At 5 kR stem length ceased to increase after either 20 to 25 
days postirradiation at 6.25 and 12.5 R/min or 5 to 7 days at 25 and 50 R/min. 
Stem length at maturity (54 days postirradiation) at 2.5 kR was approximately 
50% of the controls and was unaffected by the various rates used. Stem length at 
maturity at 5 kR was 45 and 38% of control at 6.25 and 12.5 R/min and 19 and 



EXPOSURE-RATE EFFECTS 



281 




20 30 40 

TIME AFTER IRRADIATION, days 



60 



Fig. 3 The effects of 2.5 and 5.0 kR of Co gamma radiation, as influenced 
by exposure rate, on (1) the increase in stem length vs. time after irradiation 
and (2) stem length at maturity (54 days post irradiation) in Kent soybean 
plants irradiated at 12 days postemergence. 





Exposure, 


Exposure rate, 


Symbol 


kR 


R/min 


• 








o 


2.5 


6.25* 


■ 


5 


6.25 


a 


5 


12.5 


A 


5 


25 


A 


5 


50 



*There was no difference among exposure rates at 2.5 kR; therefore a 
single curve is shown. 



14% of control at 25 and 50 R/min, respectively. Thus it appears that for 
indexes 1 and 2 an exposure-rate saturation had been attained by 25 R/min. 

The third index of radiation response of these plants, yield, is shown in 
Fig. 4. Results of an analysis of variance indicate that at 2.5 kR yield was greater 



282 



CONSTANTIN, KILLION, AND SIEMER 



100 



80 



60 



40 



20 




2.5 kR 



5.0 kR 



6.25 



50 



EXPOSURE RATE, R mm 



Fig. 4 The effects of 2.5 and 5.0 kR of Co gamma radiation, as influenced 
by exposure rate, on the yield of Kent soybean plants irradiated at 12 days 
postemergence. 



at 6.25 R/min (P<0.05) than at either 12.5, 25, or 50 R/min. This indicates 
that yield at this exposure showed a rate saturation at 12.5 R/min. However, at 
5.0 kR there was no difference in yield at P < 0.05 between plants exposed at 
6.25 and 12.5 R/min, and at 25 and 50 R/min there was essentially no yield. 

Results of experiments with split vs. continuous irradiation are shown in 
Table 1. The split exposures were done at a rate of 50 R/min, and the 
radiation-free periods were 30, 60, and 120 min. Rates for continuous exposures 
varied in accordance with total time of the different split-exposure treatments. 
Neither the duration of the radiation-free period in split exposures nor the 
exposure rate in continuous exposures caused any differences in the shoot dry 
weight of seedlings exposed to 2 kR (Table 1). 

In contrast to the results observed following 2-kR exposures, an increase in 
shoot dry weight was observed as the radiation-free period was extended from 
30 to 60 min at 4 kR (Table 1). An increase in radiation-free time to 120 min 
caused only a slight further increase in performance. A comparison of split vs. 
continuous exposures shows that a decrease in exposure rate (continuous expo- 
sures) from 36.4 to 20 R/min had a greater influence on seedling performance 
than did the increase in radiation-free period (split exposures at 50 R/min) from 
30 to 120 min. 



DISCUSSION 

Sparrow et al. 1 ° emphasized that a large biological effect can be produced in 
one species by the same dose or dose rate that produces a negligible effect in 






EXPOSURE-RATE EFFECTS 



283 



Table 1 

SHOOT DRY WEIGHT OF HILL SOYBEAN SEEDLINGS AS 

INFLUENCED BY 2 AND 4 kR OF 60 Co GAMMA RAYS ADMINISTERED 

EITHER AS A SPLIT OR A CONTINUOUS EXPOSURE* 





Exposure 


Radiation-free 


Exposure 


Shoot 


Type of 


rate, 


period, 


period, 


dry weight, t 


exposure 


R/min 


min 


min 


% of control 






2 kR 






Split 


50 


30 


70 


88.1 ±2.8 


Continuous 


28.6 





70 


84.3 ±6.2 


Split 


50 


60 


100 


81.2 ±4.1 


Continuous 


20 





100 


88.3 ± 3.4 


Split 


50 


120 


160 


86.7 ±5.8 


Continuous 


15.4 





160 


86.8 ± 5.5 



4 kR 



Split 


50 


30 


110 


15.9 ±2.4 


Continuous 


36.4 





110 


15.5 ± 1.4 


Split 


50 


60 


140 


34.4 ± 3.2 


Continuous 


28.6 





140 


42.6 ±4.3 


Split 


50 


120 


200 


39.5 ± 3.2 


Continuous 


20.0 





200 


60.3 ± 3.3 



* Exposure rates were adjusted to provide the same total duration of 
irradiation. 

tValues are the mean per treatment ± standard error. 



another species. In a later publication Sparrow et al. 1 ] demonstrated the range 
in exposures (acute) and in exposure rate (roentgens per day for chronic 
exposure) which induces lethality and/or varying degrees of growth suppression 
in a large number of species. The species response was correlated to average 
interphase chromosome volume, and it was shown that on the basis of absorbed 
energy (electron volts) per interphase chromosome the species do not vary for 
comparable levels of damage. By extrapolation one could infer that this 
relation would hold true for exposure-rate effects observed during acute 
irradiations on the basis of energy absorbed per interphase chromosome per 
minute instead of per day. Thus sensitive species would undergo a saturation at 
lower exposure rates than tolerant species when considered in terms of roentgens 
rather than electron volts absorbed. Recently Bottino and Sparrow have 
reported a constant ratio of 1.4 between simulated-fallout-decay rate over a 
36-hr period and 16-hr constant-rate exposures for lethality and yield reduction 
in plants of eight species. Furthermore, they reported that 8-hr constant-rate 
exposures were equal to the simulated-fallout-decay rate for the eight species. 



284 CONSTANTIN, KILLION, AND SIEMER 

The results presented here for soybean seedlings indicate a rate saturation at 
approximately 50 R/min for seedling studies (Fig. 1) and 25 R/min for stem 
length at maturity and for yield (Figs. 3 and 4) — two different types of end 
points. It should be noted, however, that these data were obtained from 
experiments with different varieties of plants at slightly different stages of 
development. If we can assume that varietal differences will be minimal, then we 
can infer an effect of stage of development and/or end point on the 
rate-saturation phenomenon. 

Our results concur with those of McCrory and Grun, who have reported a 
relation between dose and dose rate in diploid, hybrid clones of Solarium. A 
similar relation between dose and dose rate and end point and dose rate has been 
reported in experiments with mice. 5 Cromroy 1 2 alluded to the problems created 
by dose-rate effects when cross comparisons are made either within or among 
species. Krebs and Leong concluded from recent experiments with mice that 

(1) there was no change in LD 50 / 4 when exposure rate was 3500 R/hr or higher, 

(2) LD 50 / 4 practically doubled with a decrease from 3500 to 400 R/hr, and (3) 
there was little or no change in LD 50 / 4 when exposure rate was below 400 R/hr. 
The limited data we have on D 5 at different rates (results in this report and 
unpublished data) indicate a trend similar to conclusions 1 and 2 above. We have 
too few D 50 values for rates below 10 R/min to determine whether our results 
will also show a plateau response at low rates. Results in Fig. 1 indicate that a 
plateau may be reached; however, Fig. 1 shows the response instead of the 
exposure required to induce a particular level of response. 

A rate-saturation constant for species of organisms based on their interphase 
chromosome volume would be valuable to explain certain radiobiological 
phenomena. Cromroy reports the interphase chromosome volume of labora- 
tory white mice as approximately 2.25 (d 3 , and the results of Krebs and Leong 1 3 
indicate for the mouse a rate saturation at 3500 R/hr for LD 50 /4 caused by 
gastrointestinal damage. Hill soybean seedlings at 2 days postemergence have an 
interphase chromosome volume of 2.95 /i 3 and show a rate saturation at 
approximately 50 R/min for exposure required to reduce shoot dry weight to 
50% of control. For end points scored later in the life cycle of the plant, 
however, a rate saturation was reached at 25 R/min. Also, the Solatium hybrids 
used by McCrory and Grun 2 have an interphase chromosome volume of 6.48 Li 
and show a rate saturation at 70 R/min for lethality at an exposure of 9 kR. 
Further research may be justified because it is known that some interspecific 
hybrids deviate from expected radiosensitivity based on their interphase 
chromosome volume. 1 Sparrow et al. have shown that the required energy 
absorbed per interphase chromosome varies within a species in accordance with 
the end point and level of response. It is known also that changes in nuclear and 
interphase chromosome volumes occur during the mitotic cycle of cells and 
with seasonal changes in forest trees. 1 5 

The data in Table 1 for split vs. continuous exposures for the same length of 
time indicate that repair takes place in the soybean seedling. This does not 



EXPOSURE-RATE EFFECTS 285 

preclude the occurrence of recovery in the plant after irradiation. Table 1 data 
show a lack of a detectable repair at 2 kR with either split exposures or lowering 
the rate from 28.6 to 15.4R/min. Also, there was no difference in shoot dry 
weight between split and continuous exposures delivered during the same time 
period. This agrees with the results in Fig. 2, which indicate the lack of an 
exposure-rate effect at 2 kR and also with results in the literature. 5 ' ' 

At 4 kR an increase in shoot dry weight was observed with an increase in 
radiation-free time from 30 to 60 min, and an extension to 120 min caused only 
a slight further increase. It is inferred that repair processes reached a maximum 
expression within approximately 60 min for the conditions of exposure and 
exposure rate used. Apparently changes in exposure and exposure rate in 
split-exposure experiments would alter the extent of repair and the time during 
which it occurs (refer to Krebs and Leong for data on mice). Results with 
exposures of 4 kR at 50 R/min (Figs. 1 and 2) and at 50 R/min split exposure 
with 30 min of radiation-free time are approximately equal; this indicates that 
little repair occurred during a 30-min period. Contrary to most results in the 
literature, we observed a greater increase in shoot dry weight (from 15.5 to 
60.3% of control) by decreasing exposure rate from 36.4 to 20 R/min than that 
for split exposures with a radiation-free period of 60 and 120 min (Table 1). 
Since we have only the results of this experiment without any knowledge of the 
repair mechanism, it appears that further discussion of the phenomenon in the 
soybean seedling is unwarranted at this time. 

One last comment is warranted concerning a problem pertinent to research 
involving growth of seedlings (fresh and dry weight or stem length) following 
irradiation. Results shown in Fig. 3 demonstrate the fallacy inherent to a 
comparison of the data from experiments scored at different arbitrary times 
after treatment. To illustrate the point, consider the differences in stem length 
among plants of the various treatments when it was measured at intervals from 5 
to approximately 25 days after irradiation. The response shows minimal effects 
of exposure and rates at 5 days and maximal effects from 25 days on. The time 
course of events would probably vary according to when the organism was 
irradiated, the species, and the environmental conditions. 



ACKNOWLEDGMENTS 



The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U. S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was supported by funds from the U. S. Office of Civil Defense and 
is published with the permission of the Dean of the University of Tennessee 
Agricultural Experiment Station, Knoxville. 



286 CONSTANTIN, KILLION, AND SIEMER 

REFERENCES 

l.S. Hornsey and T. Alper, Unexpected Dose-Rate Effect in the Killing of Mice by 
Radiation, Nature, 210: 212-213 (1966). 

2. G. J. McCrory and P. Grun, Relationship Between Radiation Dose Rate and Lethality of 
Diploid Clones of Solanum, Radiat. Bot., 9(1): 27-32 (1969). 

3. A. P. Casarett, Radiation Biology, pp. 244—247, Prentice-Hall, Inc., Englewood Cliffs, 
N. J., 1968. 

4. G. A. Sacher, Reparable and Irreparable Injury: A Survey of the Position in Experiment 
and Theory, in Radiation Biology and Medicine, Walter C. Claus (Ed.), pp.283 — 313, 
Addison-Wesley Publishing Company, Inc., Reading, Mass., 1958. 

5. P. J. Bottino and A. H. Sparrow, Comparison of the Effects of Simulated Fallout Decay 
and Constant Exposure Rate Treatments on the Survival and Yield of Agricultural 
Crops, in Proceedings of the 4th International Congress of Radiation Research, Evian, 
France, p. 30 (Abstract), 1970. 

6. M. J. Constantin, The Relative Advantages of Fast Neutron Irradiation to Induce Bud 
Sprouts in Ornamental Plants, in Proceedings of the 4th International Congress of 
Radiation Research, Evian, France, in preparation, 1970. 

7. P. Pereau-Leroy, Facteurs affectant la de'chimerisation par irradiation gamma chez 
l'oeillet, Bulletin de la societe botanique de France, Colloque de morphologie 
experimentale, pp. 55—60 (1967). 

8. A. H. Sparrow, Comparisons of the Tolerances of Higher Plant Species to Acute and 
Chronic Exposures of Ionizing Radiation, Jap. J. Genet., 40(Supplement): 12 — 37 
(1965). 

9. A. H. Sparrow and L. Puglielli, Effects of Simulated Radioactive Fallout Decay on 
Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat. Bot., 9(2): 77-92 
(1969). 

10. A. H. Sparrow, R. L. Cuany, J. P. Miksche, and L. A. Schairer, Some Factors Affecting 
the Responses of Plants to Acute and Chronic Radiation Exposures, Radiat. Bot., 1(1): 
10-34(1961). 

11. A. H. Sparrow, R. C. Sparrow, K. H. Thompson, and L. A. Schairer, The Use of Nuclear 
and Chromosomal Variables in Determining and Predicting Radiosensitivities, from 
Technical Meeting on the Use of Induced Mutations in Plant Breeding, Rome, 1964. 
[Radiat. Bot., 5 (Supplement): 101-132 (1965)] . 

12. H. L. Cromroy, Mammalian Radiosensitivity. Final Report for the Office of Civil 
Defense, Contract Number N00228-68-C-2658, p. 22, 1969. 

13. J. S. Krebs and G. F. Leong, Effect of Exposure Rate on the Gastrointestinal LD 5 q of 
Mice Exposed to 6 °Co Gamma Rays or 250 kVp X-Rays, Radiat. Res., 42: 601-613 
(1970). 

14. H. Swift, Quantitative Aspects of Nuclear Nucleoproteins, Int. Rev. Cytol., 2: 1 — 76 
(1953). 

15. F. G. Taylor, Jr., Nuclear Volume Changes in Southeastern Tree Species Before Spring 
Growth, Radiat. Bot., 5(1): 61-64 (1965). 



EFFECTS OF ACUTE GAMMA IRRADIATION 
ON DEVELOPMENT AND YIELD OF 
PARENT PLANTS AND PERFORMANCE 
OF THEIR OFFSPRING 



E. G. SIEMER,* M. J. CONSTANTIN, and D. D. KILLION 

UT— AEC Agricultural Research Eaboratory, Oak Ridge, Tennessee 



ABSTRACT 

The effects of acute gamma irradiation on the development and yield of soybean, rice, and 
corn plants were determined. Plants were grown in containers outdoors and exposed once 
during their life cycle to Co gamma radiation at 50 R/min. Performance of their offspring 
was determined under greenhouse conditions. 

Yield of soybean plants receiving 2.5 kR was either unaffected or reduced to 
approximately 50% of control depending on their stage of development when irradiated. At 
early bloom 1 kR reduced yield significantly and 3 kR eliminated it. Two weeks later, 
during late bloom, 2 kR reduced yield significantly and 6 kR eliminated it. Branch 
abscission was a factor in the reduction of seed yield in soybeans. 

Yield of rice plants exposed to 25 kR was either reduced or eliminated depending on the 
stage of development when the plants were irradiated. The plants were most sensitive to 
radiation during the time from panicle initiation to anthesis. When plants were irradiated in 
small peat pots 2 days after emergence (DAE) with minimal radiation attenuation to the 
shoot meristem, 5 kR reduced yield significantly and 15 kR eliminated it. 

An exposure of 2.5 kR essentially eliminated yield of a corn plant irradiated during the 
period from tassel initiation through silking. An exposure of 500 R reduced yield significantly 
when 1-DAE plants were irradiated in small peat pots. Periods of relative tolerance to 
gamma irradiation were observed during early vegetative phase when sucker proliferation 
occurred and just prior to pollination and fertilization. 

It appears that, if the parent plant produces seed when it is irradiated prior to 
fertilization and embryogenesis, emergence and seedling growth of the offspring will be 
normal. If the parent plant produces seed when it is irradiated after fertilization, however, 
emergence and seedling growth of the offspring will reflect the decrease in sensitivity of the 
developing embryo. 



*Present address: Mountain Meadow Research Center, Colorado State University, 
Gunnison, Colo. 

287 



288 SIEMER, CONSTANTIN, AND KILLION 

The degree of damage suffered by food-crop plants subjected to radioactive 
fallout from nuclear war would depend on many factors, including kinds of 
radiation, exposure, exposure rate, stage of plant development, and environ- 
mental conditions. ' Irradiation may either inhibit or alter development of the 
vegetative and reproductive structure of the parent plant and development of the 
embryo and food-storage tissues in the seed. These factors contribute to making 
seed yield, the primary end product of agronomic food crops, relatively sensitive 
to ionizing radiation. Bell and Cole 3 referred to the lack of information 
pertinent to the prediction of the magnitude of yield reduction to be expected if 
crop plants were subjected to radioactive fallout. Tn this report we present data 
to show the effects of exposure and stage of development on the yield of corn, 
rice, and soybean plants exposed once during their life cycle to Co gamma 
radiation. Morphogenetic data for nonirradiated (control) and irradiated 
populations of plants are presented to help explain the degree of yield reduction 
observed. Data on emergence and growth of offspring are presented also to assess 
the effects of irradiation on the establishment of a crop the following year. 

MATERIALS AND METHODS 

Plants of corn (Zea mays L/WF-9 X 38-11'), rice (Oryza sativa L.'CI- 
8970-S'), and soybean [Glycine max (L.) Merrill 'Hill' and 'Kent'] were grown 
to maturity under outdoor conditions in containers (55-gal drums cut in half 
crosswise). The growth medium was a soil : Perlite : peat mixture (2:2:1 by 
volume) for the 1968 studies, and a soil : Perlite : peat : sand mixture 
(2:3:1:1 by volume) for the 1969 studies. Nitrogen, phosphorus, and 
potassium were added to maintain vigorous plant growth, and the plants were 
irrigated as needed. 

All irradiations were done at the 60 Co variable-dose-rate irradiation facility 
of the UT— AEC Agricultural Research Laboratory. Since young seedlings of 
corn and rice have their shoot meristem below ground level, when they were 
irradiated, the metal container, growth medium, and water attenuated the 
gamma radiation that reached the shoot meristem. Dosimetry indicated that the 
extent of radiation attenuation was approximately 65% at a vertical depth of 
2.5 cm and that the attenuation increased sharply within the first centimeter 
below the surface. (The attenuation was caused by the horizontal rather than the 
vertical distance through the medium traversed by the radiation.) The shoot 
meristem of corn and rice reached the surface approximately 3 weeks after 
emergence, and thereafter there was no problem of radiation attenuation by the 
medium. To study the response of young seedlings of corn and rice without the 
problem of attenuation, we grew and irradiated seedlings in small peat pots and 
then transplanted them into the containers. Attenuation was less than 10% for 
plants in these experiments. The root system of all plants received less radiation 
than did the aboveground parts. 



EFFECTS OF ACUTE GAMMA IRRADIATION 289 

Emergence and growth of the offspring from seeds harvested from parent 
plants subjected to different radiation treatments were determined in greenhouse 
benches using the same growth medium as in the containers. 

The development of control plants was studied in detail by dissection of 
three or more plants at each time of irradiation. Data were collected on the 
growth of the vegetative and reproductive structures of the plant, and the time 
of occurrence of such events as flower-bud initiation, anthesis, fertilization, etc., 
was noted. 

More-specific details concerning methodology are included in the presenta- 
tion of results for each crop. 



RESULTS 

Soybeans 

Results of the 1968 studies with Hill soybean plants are shown in Table 1. 
The length of the primary stem was affected most severely during the period from 
3 to 24 days after emergence (DAE); the extent of damage decreased with time 
from 24 to 41 DAE, and, from 45 to 62 DAE, stem length of the irradiated 
plants was greater than that of the control plants. Bean yield was affected most 
severely when the plants were irradiated at their earliest seedling stages and at 
the time of early blooming. As the plant developed its vegetative structures 
during the period from 3 to 17 DAE, it became more resistant to gamma 
irradiation. The plant became increasingly sensitive to gamma radiation from the 
time of flower-bud initiation to the time of early bloom (45 DAE). Thereafter 
resistance to gamma radiation increased; this reflects the increasing tolerance of 
the developing embryo and the increase in development of the food-storage 
tissues in the seed. Studies of the offspring indicate that percent of emergence 
and growth were affected only slightly when the parent plants were exposed to 
2.5 kR at 50 R/min prior to the time of fertilization, the period from 3 to 
approximately 38 DAE. In general, percent of emergence decreased by approxi- 
mately 40% when the parent plants were irradiated during the period from 41 to 
62 DAE. A similar trend was observed for seedling growth as measured by dry 
weight of the seedling at 18 DAE. 

Data from exposure-response studies of Hill soybean plants at 46 DAE 
(early-blooming stage) and at 60 DAE (late-blooming stage) are listed in Tables 2 
and 3. Stem length showed a maximum reduction of approximately 30% at 
46 DAE even at an exposure of 10 kR; however, at 60 DAE stem length was 
increased up to 22% above the controls, and none of the exposures used caused a 
reduction. Plants exposed to 3 kR or more did not undergo senescence (i.e., they 
did not shed their leaves) at the same time as the control plants. This response 
was probably associated with the decrease and elimination of bean development. 
The number of pods per plant was reduced by 50% at approximately 5.5 kR at 



290 



SIEMER, CONSTANTIN, AND KILLION 



Table 1 



60, 



EFFECTS OF EXPOSURE OF HILL SOYBEAN PLANTS TO u "Co GAMMA RADIATION 

(2.5 kR AT 50 R/MIN) ON STEM LENGTH AND BEAN YIELD OF PARENT 

PLANTS AND ON EMERGENCE AND OVEN-DRIED WEIGHT OF OFFSPRING* 









Parents 










Length of 


Yield of 






Time of 


primary 


stem 
%of 


beans 




Offspring 




irradiation, 


Weight, t 


%of 


Emergence,! 


Weight, § 


DAE 


cmt 


control 


g control 


% 


g 


3 


23 


40 


4.6 


11 


92 


0.091 


4 


28 


49 


5.0 


12 


96 


0.068 


6 


24 


42 


11.6 


29 


96 


0.066 


7 


26 


46 


11.4 


28 


84 


0.064 


10 


25 


44 


7.0 


17 


72 


0.058 


11 


23 


40 


24.0 


59 


84 


0.090 


12 


25 


44 


10.0 


25 


88 


0.073 


13 


24 


42 


19.0 


47 


88 


0.076 


14 


26 


46 


21.0 


52 


88 


0.084 


17 


27 


47 


30.0 


74 


96 


0.082 


20 


29 


51 


22.0 


54 


84 


0.070 


24 


17 


30 


18.1 


45 


88 


0.072 


27 


33 


58 


22.4 


55 


64 


0.084 


31 


29 


51 


11.0 


27 


92 


0.090 


34 


37 


65 


16.0 


40 


72 


0.078 


38 


44 


77 


10.3 


26 


96 


0.077 


41 


57 


100 


9.0 


22 


64 


0.049 


45 


53 


93 


7.3 


18 


64 


0.052 


48 


67 


118 


8.3 


21 


84 


0.059 


55 


68 


119 


22.2 


55 


60 


0.030 


62 


65 


114 


25.5 


63 


68 


0.033 


Control 


57 


100 


40.4 


100 


92 


0.072 



*Three plants per container and one container per treatment. 

tMean per plant. 

t Number of seedlings emerged divided by number of seeds planted times 100. 

§Mean oven-dried weight per seedling at 18 DAE. 



46 DAE, but at 60 DAE there was no reduction for the exposures used. The 
yield of beans at 46 DAE was negligible at 3 kR and above, whereas at 60 DAE 
yield became negligible at 6 kR and above. No beans were harvested from 
46 DAE plants, and few beans were harvested from 60 DAE plants exposed to 
6 kR or more. 

Because the soybean experiment had to be replanted two times in 1969 the 
lateness of the last planting necessitated a switch to Kent, which is a short-season 



EFFECTS OF ACUTE GAMMA IRRADIATION 



291 



Table 2 



60, 



EFFECTS OF EXPOSURE OF HILL SOYBEAN PLANTS TO ""Co GAMMA RADIATION 

(1 TO 10 kR AT 50 R/MIN) AT 46 DAE, i.e., EARLY-BLOOMING STAGE, ON STEM 

LENGTH, NUMBER OF PODS, AND BEAN YIELD OF PARENT PLANTS AND ON 

EMERGENCE AND OVEN-DRIED WEIGHT OF OFFSPRING* 









Parents 












Length of 




Yield of 






primary stem 


Number 


beans 




Offspring 


Exposure, 




%of 


We ; ejht,t 


%of 


Emergence,! 


Weight, § 


kR 


cmt 


control 


of podst 




control 


% 


g 


1 


66 


105 


89 


15.0 


52 


92 


0.068 


2 


67 


106 


139 


10.2 


35 


68 


0.057 


3 


61 


97 


109 


0.9 




72 


0.033 


4 


62 


98 


95 


<0.1 


< ,. 


20 


0.011 


5 


49 


78 


62 


<0.1 


<1 


10 


0.006 


6 


55 


87 


27 










7 


50 


79 


7 










8 


50 


79 


7 










9 


45 


71 


4 










10 


46 


73 


4 










Control 


63 


100 


101 


29.0 


100 


97 


0.066 



*Six plants per container and one container per treatment. 

tMean per plant. 

^Number of seedlings emerged divided by number of seeds planted times 100. 

§Mean oven-dried weight per seedling at 18 DAE. 



variety. Even so the plants were killed by a frost prior to complete maturity; 
thus "yield" refers to the combined weight of pods and immature beans. Data 
on plant-stage sensitivity to gamma irradiation are listed in Table 4. There was a 
greater reduction in stem length and yield at 25 DAE than at either earlier or 
later times; this is not consistent with the data from the experiments with Hill 
soybeans. The inconsistency was probably caused by the difference in the rate of 
development, i.e., time in days after emergence when the various developmental 
stages occurred. The results shown in Fig. 1 again illustrate the stage sensitivity 
of the soybean plant to gamma irradiation. Yield was reduced to 50% of control 
by 1.3 kR at 18 DAE, by 1.75 kR at 32 DAE, and by 2.1 kR at 4 and 45 DAE. 



Rice 



Plants exposed to 10 to 50 kR of gamma radiation at the time of heading 
(64 DAE) showed marked differences for a number of end points (Table 5). 
Irradiation had no effect on the number of panicles per plant because the 



292 



SIEMER, CONSTANTIN, AND KILLION 



Table 3 



60. 



EFFECTS OF EXPOSURE OF HILL SOYBEAN PLANTS TO Co GAMMA RADIATION 

(1 TO 10 kR AT 50 R/MIN) AT 60 DAE, i.e., LATE-BLOOMING STAGE. ON STEM 

LENGTH, NUMBER OF PODS, AND BEAN YIELD OF PARENT PLANTS 

AND ON EMERGENCE AND OVEN-DRIED WEIGHT OF OFFSPRING* 









Parents 












Length of 




Yield of 






primary stem 


Number 


beans 


Offspring 


Exposure, 




%of 


Weigh t,t 


% of 


Emergence,! 


Weight, § 


kR 


cmt 


control 


of podst 


g 


control 


% 


g 


1 


73 


116 


89 


20.0 


69 


100 


0.066 


2 


70 


111 


169 


18.0 


62 


68 


0.111 


3 


75 


119 


217 


16.0 


55 


52 


0.026 


4 


73 


116 


168 


6.7 


23 


36 


0.010 


5 


76 


121 


170 


5.1 


18 


28 


0.010 


6 


73 


116 


133 


<0.1 


<1 


29 


0.006 


7 


73 


116 


122 


<0.1 


<1 






8 


63 


100 


122 


<0.1 


<1 






9 


77 


122 


123 


<0.1 


<1 






10 


67 


106 


98 


<0.1 


<1 






Control 


63 


100 


101 


29.0 


100 


97 


0.066 



*Six plants per container and one container per treatment. 

tMean per plant. 

^Number of seedlings emerged divided by number of seeds planted times 100. 

§Mean oven-dried weight per seedling at 18 DAE. 



maximum number of panicles per plant had been developed before irradiation. 
Grain yield was reduced to approximately 50% of the control by exposures of 
10 to 30 kR. It was noted also that the average oven-dried weight per grain was 
unaffected by the radiation exposure (data not shown). Performance of the 
offspring was determined by planting random samples of grain from each 
treatment. Emergence was unaffected by 10 kR, reduced to approximately 50% 
of control by 20 kR, and reduced to 0% by 40 and 50 kR. The pattern of 
response for seedling growth was similar to that for emergence. 

Plants in the 1969 studies were exposed once in their life cycle to 25 kR at 
50 R/min, and the data are shown in Table 6. The plant's stage of development 
at the time of irradiation influenced the response observed. Yield of grain 
declined sharply in plants irradiated after 10 DAE and was reduced to zero in 
plants exposed at 3 7 to 57 DAE. Plants exposed at 65 DAE yielded approxi- 
mately 65% of control, which was somewhat higher than expected on the basis 
of results obtained the previous year (see Table 5). The performance of plants 
exposed at 4 and 10 DAE was influenced by radiation attenuation because their 
shoot meristem was below ground level. 



EFFECTS OF ACUTE GAMMA IRRADIATION 



293 



Table 4 

EFFECTS OF 2.5 kR OF 6 °Co GAMMA RADIATION AT 
50 R/MIN ON STEM LENGTH AND YIELD* OF KENT SOYBEAN PLANTSt 







Length 


of 






Time of 


primary 


stem 


Yield 




irradiation, 






%of 


Weight, § 


%of 


DAE 


cm| 




control 


g 


control 


4 


50 




88 


7.4 ±0.8 


41 


12 


37 




65 


6.7 ±0.9 


37 


18 


38 




67 


1.1 ±0.3 


6 


25 


35 




61 


0.3 ±0.2 


2 


31 


42 




74 


2.7 ±0.4 


15 


37 


47 




83 


6.8 ±0.8 


37 


44 


50 




87 


6.1 ±0.4 


34 


50 


54 




94 


14.2 ±0.7 


78 


Control 


57 




100 


18.2 ± 1.1 


100 



*"Yield" refers to oven-dried weight of pods and immature beans. 
tThree plants per container and three containers per treatment. 
JMean length per plant. 
§ Mean per plant ± one standard error of the mean. 




Fig. 1 Response curves for Kent soybean plants exposed to Co gamma 
radiation at different days after emergence, showing the effects of from 1 to 
4 kR at 50 R/min on yield. ("Yield" refers to oven-dried weight of pods and 
immature beans.) There were three plants per container and three containers 
per treatment. •, 4 DAE; O, 18 DAE; □, 31 DAE; A, 45 DAE;^, standard error. 



Table 5 



60, 



EFFECTS OF EXPOSURE* OF CI-8970-S RICE PLANTS TO ""Co GAMMA RADIATION 

(10 TO 50 kR AT 50 R/MIN) AT 64 DAE, i.e., TIME OF PANICLE EMERGENCE, 

ON NUMBER OF PANICLES AND GRAIN YIELD OF PARENT PLANTS AND ON 

EMERGENCE AND WEIGHT OF OFFSPRINGt 







Parents 






Offsprii 






Number of 


Grain 


yield 


*g 


Exposure, 


Weight,! 


%of 


Emergen 


ce,§ 


Weight, % 


kR 


paniclest 


g 


control 


% 




g 


10 


24 


3.7 


41 


89 




0.017 


20 


25 


4.4 


49 


57 




0.015 


30 


19 


4.3 


48 


32 




0.009 


40 


17 


0.7 


8 









50 


20 


1.9 


21 









Control 


22 


9.0 


100 


93 




0.032 



*Data from the 1968 studies. 

tFive plants per container and one container per treatment. 

±Mean per plant. 

§ Number of seedlings emerged divided by number of seeds planted times 100. 

1|Oven-dried weight per seedling at 7 DAE. 



Table 6 



6 , 



EFFECTS OF EXPOSURE* OF CI-8970-S RICE PLANTS TO ""Co GAMMA RADIATION 

(25 kR AT 50 R/MIN) ON GRAIN YIELD OF PARENT PLANTS AND ON EMERGENCE 

AND WEIGHT OF OFFSPRINGt 





Parents 






Offspri 




Time of 


Grain yield 




n g 


irradiation. 


Weight, t 


%of 


Emergence, § 




Weight, H 


DAE 


g 


control 


% 




g 


4 


16.4 ± 5.7 


63 


92.0 ±2.4 




0.069 ±0.005 


10 


11.9 ±4.3 


46 


88.7 ±2.4 




0.076 ±0.003 


17 


2.6 ±0.6 


10 


89.1 ±2.6 




0.068 ±0.004 


24 


4.0 ±0.6 


15 


84.1 ± 3.1 




0.072 ±0.007 


31 


2.6 ±1.1 


10 


82.4 ± 1.6 




0.067 ±0.005 


37, 52, 57 















65 


16.5 ± 3.6 


64 


74.1 ±2.4 




0.012 ±0.050 


80 


37.8 ±3.5 


146 


59.5 ± 3.1 




0.009 ±0.001 


Control 


25.9 ±9.1 


100 


91.6 ±0.7 




0.070 ±0.005 



*Data from the 1969 studies. 

tFour plants per container and three containers per treatment. 

xMean per plant ± one standard error. 

§Mean of four replications ± one standard error; 60 seeds planted per replication. 

fMean fresh weight per survivor at 8 DAE ± one standard error. 



EFFECTS OF ACUTE GAMMA IRRADIATION 



295 



Emergence and fresh weight of the offspring were unaffected when the 
parent plants were exposed to 25 kR at 50 R/min before fertilization and 
embryogenesis. In contrast, at 65 and 80 DAE emergence and fresh weight per 
seedling decreased significantly. 

Exposure-response curves for plants at 2, 31, and 65 DAE are shown in 
Fig. 2. The 2-DAE plants were irradiated in small peat pots, and the shoot 
meristem of 31- and 65-DAE plants was above ground level; therefore radiation 




10 



15 20 

EXPOSURE, kR 



Fig. 2 Response curves for CI-8970-S rice plants exposed to Co gamma 
radiation at different days after emergence, showing the effects of from 5 to 
35 kR at 50 R/min on grain yield. The 2-DAE plants were growing in small 
peat pots, and the 31- and 65-DAE plants had their shoot meristem above the 
surface of the medium; therefore radiation attenuation was minimal in all 
cases. There were four plants per container and three containers per treatment. 
•, 2 DAE; O, 31 DAE; A, 65 DAE; J, standard error. 



attenuation was minimal in all cases. An exposure of 10 kR reduced yield of 
grain in 2- and 31-DAE plants to such an extent that it would have been 
impractical to harvest the crop. The 65-DAE plants showed a higher tolerance to 
gamma radiation than did the 2- and 31-DAE plants. However, the extent of 
variability was high for those plants, and the only conclusion one can make is 
that 5 kR did not reduce yield of grain, whereas 15, 25, and 35 kR caused a 
significant reduction. The emergence and oven-dried weight of offspring from 
parent plants irradiated at 2, 31, and 65 DAE are shown in Figs. 3 and 4, 
respectively. Emergence was unaffected when the parent plants were exposed to 
either 5 and 10 kR at 2 DAE or 5 to 30kR at 31 DAE; however, emergence 
decreased steadily as exposure increased when the parent plants were irradiated 
at 65 DAE. The D 50 for emergence of offspring was approximately 10 kR, and 



296 



SIEMER, CONSTANTIN, AND KILLION 




15 20 

EXPOSURE, kR 



60, 



Fig. 3 Response curves for CI-8970-S rice plants exposed to "Co gamma 
radiation at different days after emergence, showing the effects of from 5 to 
35 kR at 50 R/min to parent plants on percent emergence of their offspring. 
Sixty seeds were planted for each of four replications in a randomized block 
design. •, 2 DAE;0, 31 DAE; A, 65 DAE;"]", standard error. 



140 




15 20 

EXPOSURE, kR 



Fig. 4 Response curves for CI-8970-S rice plants exposed to Co gamma 
radiation at different days after emergence, showing the effects of from 5 to 
35 kR at 50 R/min to parent plants on oven-dried weight of their offspring at 
7 DAE. Sixty seeds were planted for each of four replications, and the average 
weight per survivor is presented as percent of control. •, 2 DAE; C, 31 DAE; 
A, 65 DAE; ~[ , standard error. 



EFFECTS OF ACUTE GAMMA IRRADIATION 



297 



there was no emergence at 35 kR when the parent plants were irradiated at 
65 DAE. Dry weight of the offspring from parent plants irradiated at 2 DAE 
decreased to approximately 75% of control at 10 kR, the highest exposure at 
which viable grains were harvested. Dry weight of the offspring from parent 
plants irradiated at 31 DAE decreased to approximately 65% of control at 
30 kR, the highest exposure used. Dry weight of the offspring of parent plants 
irradiated at 65 DAE showed a linear decrease vs. exposure; at 25 kR their 
performance was approximately 20% of control, whereas at 35 kR there was no 
emergence. The D 50 was approximately 12.5 kR. 

Corn 

The effect of stage of development on the yield of grain of WF-9 X 38-11 
corn plants exposed to 2.5 kR at 50 R/min is shown in Fig. 5. Results from 
studies conducted in 1968 and 1969 indicated little or no difference attributable 
to year effects. An exposure of 2.5 kR caused an increasing reduction in grain 
yield as the plant progressed through the early stages of vegetative development. 



140 




30 40 50 60 70 

DAYS AFTER EMERGENCE 



00 



60. 



Fig. 5 Response curves for WF-9 x 38-11 corn plants exposed to Co 
gamma radiation at different days after emergence, showing the effects of 
2.5 kR at 50 R/min on the grain yield per plant. In the 1968 studies there 
were two plants per container and three containers per treatment; in 1969 
there were three plants per container and three containers per treatment. The 
time of tassel initiation was 22 and 19 DAE, top ear initiation was 32 and 
30 DAE, and silking was 55 and 49 DAE in 1968 and 1969, respectively. O, 
1968; •, 1969;^, standard error. 



298 



SIEMER, CONSTANTIN, AND KILLION 



Radiation attenuation may have caused the observed response because the shoot 
meristem of the corn plant became progressively closer to the soil surface during 
this period. Yield of grain decreased to zero following 2.5 kR to plants irradiated 
from the time of transition of the shoot apex from the vegetative to the 
reproductive phase through the initiation and development of ear and tassel 
primordia. The generally increased yield of grain of plants irradiated at later 
successive stages after fertilization reflects the increasing tolerance of the 
developing embryo. Data on the response of the various morphological end 
points that contribute to yield of grain are listed in Table 7, and in general, their 



Table 7 



60. 



EFFECTS OF EXPOSURE* OF WF-9 x 38-11 CORN PLANTS TO Co 

GAMMA RADIATION (2.5 kR AT 50 R/MIN) ON VARIOUS 
MORPHOLOGICAL END POINTS CONTRIBUTING TO GRAIN YIELDt 



Time of 


Ear 


Seeded ear 


Number of 


Kernel 


irradiation, 


length,! 


length, + 


kernels per 


weight, § 


DAE 


cm 


cm 


ear$ 


g 


1 


19.0 


16.7 


416 


0.26 


2 


16.6 


13.7 


313 


0.25 


3 


16.7 


13.0 


130 


0.27 


6 


15.8 


12.1 


92 


0.29 


7 


17.0 


14.1 


330 


0.25 


8 


11.4 


9.9 


132 


0.24 


9 


13.2 


11.4 


72 


0.14 


10 


14.0 


12.0 


106 


0.13 


13 


14.0 


7.5 


103 


0.10 


14 


15.6 


8.6 


73 


0.10 


15 


11.0 


4.5 


30 


0.07 


20 


8.5 


7.0 


33 


0.08 


27-4811 










52 


13.1 


11.5 


246 


0.16 


55 


14.3 


12.0 


273 


0.13 


59 


18.1 


15.3 


368 


0.08 


62 


17.2 


13.7 


360 


0.09 


66 


19.6 


16.1 


545 


0.18 


69 


20.3 


15.5 


391 


0.24 


76 


21.0 


17.1 


552 


0.26 


83 


19.1 


17.0 


476 


0.24 


Control 


20.9 


18.6 


616 


0.25 



*Data from the 1968 studies. 

tTwo plants per container and three containers per treatment. 

± Mean per ear. 

§Mean per kernel. 

f No grain yield for six dates of irradiation. 



EFFECTS OF ACUTE GAMMA IRRADIATION 299 

responses are similar to that for grain yield. Table 8 lists the various recognizable 
morphological events in the plant's life cycle as they occurred vs. days after 
emergence. 

The relatively high yield of grain observed when 7- and 10-DAE plants were 
irradiated in 1968 and 1969, respectively, probably reflects a radiation-tolerant 
stage of development, namely, initiation and development of primary axillary 
buds or suckers. Some irradiated plants developed as many as three primary 
suckers that produced ears and a measurable amount of grain. Likewise, the 
relatively high yield of grain observed in 5 5- and 48-DAE plants irradiated in 

Table 8 

PROGRESSIVE MORPHOLOGICAL DEVELOPMENT OF CONTROL 
WF-9 x 38-1 1 CORN PLANTS* 







Days after 


emergence 


Event 




1968 


1969 


Accelerated growth in upstretched leaf height 


1 to 55 


1 to 49 


Tassel initiation 




22 


19 


Terminal shoot growing point at soil surface 


23 


19 


Accelerated stem elongation 




31 to 5 5 


21 to 55 


Ear 1 (top ear) initiation 




32 


30 


Ear 2 initiation 




33 


32 


Accelerated tassel elongation 




34 to 44 


29 to 43 


Full potential of kernel primordia 








established, ear 1 




44 




Total blade length achieved 




45 




Accelerated tassel peduncle elongation 




48 to 5 5 


40 to 51 


Accelerated ear 1 elongation 




48 to 62 


40 to 58 


Tassel emergence 




52 


43 


Anthesis 




55 


50 


Very early silking 




55 


49 



*Data were collected by dissecting control plants grown concurrently with 
other plants that were irradiated at different days after emergence. 

1968 and 1969, respectively, probably reflects a stage of relative tolerance to 
gamma rays. Megagametogenesis had occurred by this time, and the egg was 
mature. Microgametogenesis had also occurred; however, we have no means of 
evaluating the effects of irradiation on pollen, because pollen from control 
plants was available for pollination. 

To test the sensitivity of WF-9 X 38-11 corn plants to gamma radiation 
without the complication of radiation attenuation, we irradiated plants in small 
peat pots and then transplanted them to containers. The results are shown in 
Fig. 6. Yield of grain showed a linear decrease with exposure and was reduced to 
zero at 2.5 kR. The D 50 for yield of grain was approximately 750 R. This 



300 



SIEMER, CONSTANTIN, AND KILLION 



100 




I I I 


80 










60 






— 












40 






— 


20 
n 




I 


i ^\ 



0.5 



1.0 1.5 

EXPOSURE, kR 

60, 



2.0 



2.5 



Fig. 6 WF-9 x 38-11 corn plants exposed to Co gamma radiation at 1 DAE 
in small peat pots; radiation attenuation at the shoot meristem was minimal. 
The response curves show the effect of 0.5 to 2.5 kR at 50 R/min on grain 
yield of the parent plants and emergence and weight of their offspring. Data 
are from the 1969 studies. •, yield; O, fresh weight of offspring at 1 3 DAE; A, 
emergence;^, standard error. 



indicates that the decrease in tolerance in plants irradiated during their early 
seedling stage (Fig. 5) was probably caused by radiation attenuation by the 
medium. Emergence and fresh weight of the offspring of parent plants irradiated 
at 1 DAE showed little or no difference as exposure was increased to 2 kR. 

An exposure response study was conducted with WF-9 X 38-11 corn plants 
at 10 selected times after emergence. Response data are listed in Table 9; the 
pattern of response for stage of development was similar to that shown in Fig. 5. 
Plants irradiated at 22 and 36 DAE showed the highest degree of sensitivity; zero 
yield of grain was observed following exposures of 1.5 and 2 kR, respectively. 
Yield of grain showed an increased tolerance to gamma radiation when plants 
were exposed to 1.5 kR or more at 44 and 50 DAE. Plants exposed at 54 DAE, 
the zygotic and early embryonic stages, showed a relatively high sensitivity, 
which decreased with each later successive time of irradiation. 

The performance of offspring from grain harvested from irradiated parent 
plants was studied under greenhouse conditions. Response curves in Fig. 7 show 
the effects of stage of development at irradiation on the emergence and fresh 
weight of offspring from parent plants receiving 2.5 kR at 50 R/min. The 
response for both of these end points was similar to that for yield of grain for 
the irradiated parent plants. The increase in tolerance of the developing embryo 
is evident from 60 to 95 DAE. Data on the emergence and fresh weight of 
offspring from the exposure-response study are shown in Tables 10 and 11, 



EFFECTS OF ACUTE GAMMA IRRADIATION 301 



Table 9 

' WF-9 x 
GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON GRAIN YIELDt 



EFFECTS OF EXPOSURE* OF WF-9 x 38-11 CORN PLANTS TO 60 Co 



Time of 
irradiation, 






Yield weighty at 


four exposures, g 


DAE 


1.0 kR 


1.5 kR 


2.0 kR 


2.5 kR 


8 


121 


±8 


83 ±2 


68 ± 17 


51 ±21 


22 


61 


±11 











36 


57 


±17 


14±9 








44 


57 


±25 


42 ±1 


18±8 


2±2 


50 


81 


±4 


87 ±14 


63 ±2 


40 ±9 


54 


89 


±11 


44 ±9 


26 ±9 


17 ±7 


60 


50 


±49 


106 ±5 


68 ±2 


83 ±12 


65 


84 


±16 


103 ±11 


88 ±4 


106 ±3 


72 


100 


±24 


115 ±4 


107 ±8 


121 ±3 


81 


115 


±4 


110±20 


113 ± 14 


95 ±7 


Control 


95 


±19 









*Data from the 1969 studies. 

tThree plants per container and three containers at 2.5 kR and two 
containers for other exposures. 

^Mean per plant ± standard error. 

respectively. Generally, emergence showed a relatively high tolerance to gamma 
radiation, and fresh weight showed a pattern of response similar to the yield of 
grain. The increase in fresh weight of the offspring from parent plants irradiated 
at 60 to 81 DAE shows the decrease in sensitivity of the developing embryo. 



DISCUSSION 

Irradiation can reduce the vegetative mass of the plant, the photosynthetic 
factory, and in so doing can reduce the carbohydrate supply available for storage 
in seeds. Soybean plants exposed to 2.5 kR produced fewer primary stem 
internodes and leaves and fewer and shorter branches. Some leaflets were 
reduced in size. Branches abscised before and after flowering and fruiting, and 
either seed potential or seed was lost. Rice plants irradiated at 2 DAE in small 
peat pots at 5 kR showed significantly less height and tillering than control 
plants 4 weeks later. Corn plants irradiated at 1 DAE in small peat pots showed a 
reduction in size following exposure to 500 R or more gamma radiation after 
15 days. Specific irradiation effects observed in experiments included shortened 
internodes, shortened and decreased width of leaf blades, and shortened leaf 
sheaths. Others have shown that irradiation can reduce vegetative mass; e.g., the 
rice studies of Kawai and Inoshita 4 and the barley studies of Hermelin. 5 



302 



SIEMER, CONSTANTIN, AND KILLION 



140 




30 



40 50 60 70 

DAYS AFTER EMERGENCE 



80 



90 



100 



Fig. 7 Response curves for WF-9 x 38-11 corn plants exposed to Co 
gamma radiation at different days after emergence, showing the effects of 
2.5 kR at 50 R/min to the parent plants on emergence and fresh weight of 
their offspring. Data are from the 1969 studies. O, emergence; •, fresh weight 
of offspring at 13 DAE. 



Irradiation can alter the normal developmental pattern of a plant or the 
timing of developmental events and thus can reduce grain yield. Corn has been 
bred and selected for maximum yield obtained from one or at most two ears on 
a single-stemmed plant. The 2.5-kR exposures increasingly inhibited parental 
shoot development in corn as irradiation took place later after shoot emergence. 
This inhibition pattern was attributed to increased irradiation of the apical 
meristem of the parental shoot as the underground stem elongated. Increasing 
inhibition of the parental shoot permitted development of axillary shoots until 
as many as three suckers developed. However, all this vegetative proliferation 
cost time and available carbohydrates, and grain yield declined sharply with 
sucker proliferation. When parental shoots were irradiated later, the sucker buds 
did not develop, and the plant died. Sucker proliferation has been reported by 
others, including Sparrow and Puglielli for corn and Davies for wheat. 

Although the early developmental period of corn, rice, and possibly of any 
grass plant, is characterized by a decline in yield as irradiation is delayed, there is 
a period of relative tolerance to gamma irradiation. This is caused probably by 
the arrest of the primary shoot meristem which permits the development of one 
or more axillary buds that are more tolerant to gamma irradiation because of 
their developmental stage. 



EFFECTS OF ACUTE GAMMA IRRADIATION 



303 



Table 10 

EFFECTS OF EXPOSURE OF PARENT WF-9 x 38-11 CORN PLANTS 

60, 



TO 



Co GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON 
THE EMERGENCE OF OFFSPRING* 



Time of 
irradiation, 


Emergencet at four 


exposures, % of 


control 


DAE 


l.OkR 


1.5 kR 


2.0kR 


2.5 kR 


8 


97 


94 


98 


94 


22 


96 


i 


i 


t 


36 


91 


61 


t 


t 


44 


94 


86 


86 


55 


50 


79 


84 


82 


75 


54 


78 


55 


72 


63 


60 


78 


89 


69 


36 


65 


97 


98 


85 


77 


72 


98 


97 


97 


92 


81 


94 


98 


97 


84 


Control, 100% 











*Sixty seeds planted for each of three replications. 

tMean of three replications. 

JNo seed produced by parent plants. 



Table 11 



EFFECTS OF EXPOSURE* OF PARENT WF-9 x 38-11 CORN 

PLANTS TO 60 Co GAMMA RADIATION (1 TO 2.5 kR AT 50 R/MIN) ON 

FRESH WEIGHT OF OFFSPRING HARVESTED AT 13 DAE 



Time of 
irradiation, 


Fresh 


weightt at four 


exposures, % 


of control 


DAE 


1.0 kR 


1.5kR 


2.0 kR 


2.5 kR 


8 


108 


108 


100 


100 


22 


130 


t 


* 


t 


36 


77 


38 


Z 


i 


44 


85 


69 


69 


15 


50 


54 


69 


46 


35 


54 


54 


31 


39 


31 


60 


62 


46 


23 


8 


65 


85 


77 


39 


15 


72 


77 


69 


54 


39 


81 


85 


77 


62 


54 


Control, 1.3 g = 


100% 









*Data from the 1969 studies. 

tMean of three replications. 

$No seed produced by parent plants. 



304 SIEMER, CONSTANTIN, AND KILLION 

Irradiation can affect gametogenesis, the production of a functional egg and 
pollen. Hermelin found that barley is sensitive to irradiation at meiosis, and 
Kawai and Inoshita 4 found the same for rice. The exposure of soybeans to 
2.5 kR at early bloom caused severe yield reduction. The exposures of rice 
plants to 25 kR between 34 and 55 DAE (roughly from panicle initiation to 
anthesis) eliminated all grain yield. One-tenth this exposure (2.5 kR) applied to 
corn between tassel initiation and a week before silking also eliminated grain 
yield. Corn plants exposed at about the time of ear initiation (32 DAE) died. 
The adaptive nature of the corn plant when irradiated at this time became 
apparent in that tiller buds among brace roots became floral and a small amount 
of grain was produced before complete plant death. This grain would not be 
harvestable, however. Corn has the capacity to form ears from the top ear 
downward. Since each lower ear is initiated slightly after the one above it, one 
might expect that the second or third ear would take over development when 
the top ear is damaged. This sometimes happens when top ears are bagged to 
prevent premature fertilization in a breeding program but was not observed in 
our experiments. Either all axillary buds were damaged similarly or the effects of 
death in the top ear unfavorably permeated to lower ones. Plants killed by 
irradiation died from the top downward, and death was preceded by an 
accumulation of anthocyanin in the leaf tissue. 

Also, the normal corn ear is terminal; i.e., it arises on the end of the shank 
and is enclosed by husk leaves. Axillary ear buds frequently are initiated late in 
development above husk leaves, and, when the terminal ear is irradiated before 
silking, an axillary ear may eventually produce grain. 

A radioresistant stage for corn apparently exists just before silking. Plants 
irradiated at 2.5 kR within a week before the first emergence of silks produced 
relatively high grain yields; the grain had relatively high germination and 
produced relatively vigorous seedlings. This phenomenon is believed to be caused 
by the egg's having achieved full development in preparation for silk elongation, 
pollination, and fertilization. This potential to form grain might not be achieved 
in a uniform corn field where most top ears would be in a comparable 
developmental state and where irradiation eliminated viable pollen. Our material 
had viable pollen available for fertilization. Donini and Hussain found that 
irradiation was more detrimental to pollen formation than to egg formation in 
wheat. This needs to be investigated in corn. 

Gametogenesis and the flowering date of a plant can be advanced by 
irradiation. 7 We observed this when 1-DAE corn plants were exposed to 4.5 kR 
(data not presented). In our material, however, this occurred at the expense of 
building vegetative structure, and gram yield was reduced. When tiller prolifera- 
tion was encouraged by an irradiation insult to the parent shoot, the end result 
was late and incomplete ear formation. Upsetting the normal plant anthesis and 
silking pattern can reduce yields since pollen is not available when silks are 
receptive. 



EFFECTS OF ACUTE GAMMA IRRADIATION 305 

Irradiation can reduce grain yield by direct effects on the zygote, later 
embryonic plant development, and endosperm development. Mericle and 
Mericle 8 found the zygote stage in barley to be especially sensitive. The sharp 
reduction in our corn yields immediately after first silking supports this 
conclusion. 

ACKNOWLEDGMENTS 

The UT— AEC Agricultural Research Laboratory is operated by the 
Tennessee Agricultural Experiment Station for the U. S. Atomic Energy 
Commission under Contract AT-40-1-GEN-242. 

This work was funded by the Office of Civil Defense, Work Order No. DAHC 
20-69-C-0109 and is published with the permission of the Dean of the University 
of Tennessee Agricultural Experiment Station, Knoxville. 

REFERENCES 

1. A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on 
Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat. Bot., 9: 77-92 (1969). 

2. C. R. Davies, Effects of Gamma Irradiation on Growth and Yield of Agricultural Crops. 
I. Spring Sown Wheat, Radiat. Bot., 8: 17-30 (1968). 

3. M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to 
Fallout Radiation. Final Report, USAEC Report TID-24459, UT-AEC Agricultural 
Research Laboratory, Sept. 7, 1967. 

4. T. Kawai and T. Inoshita, Effects of Gamma Irradiation on Growing Rice Plants. 
I. Irradiation at Four Main Developmental Stages, Radiat. Bot., 5: 233-255 (1965). 

5. T. Hermelin, Effects of Acute Gamma Irradiation in Barley at Different Ontogenetic 
Stages, Hereditas, 57: 297-302 (1967). 

6. B. Donini and S. Hussain, Development of Embryo of Triticum durum Following 
Irradiation of Male or Female Gamete, Radiat. Bot., 8: 289-295 (1968). 

7. K. Sax, The Stimulation of Plant Growth by Ionizing Radiation, Radiat. Bot., 3: 
179-186 (1963). 

8. L. W. Mericle and R. P. Mericle, Radiosensitivity of the Developing Plant Embryo, in 
Fundamental Aspects of Radiosensitivity. Report of a Symposium Held June 5-7, 1961, 
Upton, N. Y., USAEC Report BNL-675, pp. 262-286, Brookhaven National Laboratory. 
(Brookhaven Symposia in Biology Number 14.) 



EFFECTS OF EXPOSURE TIME AND RATE 

ON THE SURVIVAL AND YIELD 

OF LETTUCE, BARLEY, AND WHEAT 



P. J. BOTTINO and A. H. SPARROW 

Brookhaven National Laboratory, Upton, New York 



ABSTRACT 

Experiments were conducted to compare the effects of 137 Cs gamma radiation given as 
either 1-, 4-, 8-, or 16-hr treatments at constant rates (CR) with 36-hr fallout-decay- 
simulation (FDS) or with buildup (Bu) and fallout-decay-simulation (Bu + FDS) treatments 
with variable exposure rates. Seedlings of lettuce were given Bu + FDS, FDS, and 1-, 4-, 8-, 
and 16-hr CR treatments. Barley and wheat seedlings were given FDS and 8- and 16-hr CR 
treatments. Following irradiation the lettuce plants were transplanted to the field, barley to 
the greenhouse, and wheat to a growth chamber. The criteria of effect used were survival 
and yield. Young barley seedlings were given a total exposure of 1600 R at 32 different 
rates ranging from 60 to 4800 R/hr. The first leaf of each seedling was measured after 
8 days of growth. 

For equal total exposures, FDS treatments were more effective than 16-hr CR 
treatments in reducing survival and yield of all three crops. The ratio of 16-hr CR to FDS at 
LD50 was 1.43 for lettuce, 1.23 for barley, and 1.3 7 for wheat. For yield the FDS was more 
effective only at exposures above the LD50. Lettuce survival increased with exposure time 
between 1 and 16 hr, but this was a linear increase only after 4 hr. Barley seedling height 
decreased as the exposure rate increased from 60 to about 1000 R/hr. Further increases in 
exposure rate above 1000 R/hr had no further effect on seedling height. The greater 
effectiveness of the high exposure rates observed in these experiments substantiates our 
conclusion that the increased effect of an FDS treatment compared with a 16-hr CR 
treatment is attributable to the high initial exposure rates of FDS. 

Similar results for survival and yield reduction for the 8-hr CR and the FDS treatments 
were observed. Hence investigators lacking the facilities to simulate fallout decay could use 
an 8-hr CR treatment to approximate the effects of simulated-fallout-decay treatments. 



For equal total exposures of gamma radiation, a treatment simulating fallout 
decay has been reported 1-3 to be more effective in reducing survival and yield of 
crop plants than are prolonged constant-exposure-rate treatments. The greater 
effectiveness of the fallout-decay-simulation (FDS) treatment is thought to be 
due to the very high exposure rates encountered initially. 1-3 Thus study of the 

306 



EFFECTS OF EXPOSURE TIME AND RATE 307 

effects of a given amount of fallout or simulated fallout radiation seems to 
become basically a problem of the effect of variations in exposure rate. This 
paper presents some of our most recent data on the effects of the gamma 
component of simulated fallout on crop plants and additional data showing how 
variations in exposure rate can affect a plant's response to radiation. These data 
give support to the conclusion that high exposure rates are the basis for the 
greater effectiveness of the fallout-decay treatments. The plants used in this 
study were lettuce, barley, and wheat. 



MATERIALS AND METHODS 

Facilities and Treatment Procedure 

The theory and facilities used to simulate fallout decay have been previously 
described in detail. 1 Basically, a series of stainless-steel shields are lowered over a 
12,000-Ci 137 Cs source at predetermined times to simulate exposure to fallout 
radiation that decays according to the t * ' law. Each shield is machined to 
reduce the intensity by one-half. The plants are placed in concentric arcs around 
the source, and an entire series of exposures is given at one time for either FDS 
or constant-rate (CR) exposures. 

Figure 1 shows the exposure-rate patterns for a total exposure of 5000 R for 
the treatments used in this study. The CR treatments simply extend for a 
specific time — in the present study this was for 1, 4, 8, or 16 hr. In the buildup 
and fallout-decay-simulation treatment (Bu + FDS), which is a close approxima- 
tion to a true fallout situation, the exposure rate starts out at a low level, builds 
up in 51 min to a peak, and then decreases in a stepwise pattern over the 
exposure period. In the FDS treatment the exposure rate starts out very high 
and decreases in a similar stepwise fashion. The steps on the buildup and decay 
curves represent shields being raised or lowered, and, although this is a stepwise 
relation, the curve for accumulating exposure is fairly smooth, as shown in 
Fig. 2. 

Experimental Procedure 

In the first experiment seedlings of lettuce, Lactuca sativa 'Summer Bibb,' 
were exposed 26 days after sowing in 2-in. peat pots to the following 
treatments: (1) CR treatments for 1, 4, 8, or 16 hr or (2) changing-exposure-rate 
treatments given as either FDS or Bu + FDS for 36 hr. Fifteen exposures of 
30 plants each, plus a nonirradiated control, were used for the 16-hr CR, FDS, 
and Bu + FDS treatments, and seven exposures of 10 plants each, plus a 
nonirradiated control, were used for the 1-, 4-, and 8-hr CR treatments. The 
experiment was carried out in early June 1969. The exposure rates for a total 
exposure of 5000 R were 5000, 1250, 625, and 312.5 R/hr for the 1-, 4-, 8-, and 
16-hr treatments, respectively. The exposure rates for other total exposures 



308 



BOTTINO AND SPARROW 



1300 



1200 



1100 



1000 



900 



800 



< 700 

LU 
D 

g 600 

Q. 
X 



500 



400 



300 



200 



100 



i i i I i i f i i I — i — i — i — i — i — i — r 



36-hr FDS 
36-hr Bu + FDS 
8-hr CR 
16-hr CR 



H 



_LJ I I I I I I I I L 



"^ 



J I L 



8 12 16 20 24 28 32 36 

TIME, hr 



Fig. 1 Exposure-rate patterns for a total exposure of 5000 R for the 
treatments used. 



EFFECTS OF EXPOSURE TIME AND RATE 



309 



16 



14 



I I I I I I I I I I I I I I 




, Theoretical fallout accumulation 

, FDS accumulation 

, Bu + FDS accumulation 



I I I I I I I I I I I I I I I ! I I I 



2 16 20 24 28 

HOURS AFTER DETONATION 



32 



36 



40 



Fig. 2 Accumulated exposures for the 36-hr FDS and 36-hr Bu + FDS at 1 m 
from the source compared with the theoretical accumulated exposures 
expected during the same period from decay according to the t law. 



varied in proportion to the exposure time. After irradiation the plants were 
transplanted to the field. Survival data were collected every other day until no 
more deaths attributable to the radiation occurred. Yield data measured as fresh 
weight of the aboveground portion of each plant were collected at the 
conclusion of the experiment. 

In December 1969 seedlings of barley, Hordeum vulgare 'Mari,' 8 days after 
sowing in 2-in. peat pots, were irradiated with the following treatments: (1) CR 
treatments for either 8 or 16 hr or (2) a changing-exposure-rate treatment given 
as a 36-hr FDS. For each treatment there were 14 exposures of 10 plants each, 
plus a nonirradiated control. After irradiation the plants were transplanted into 
6-in. clay pots and moved to a heated greenhouse. Survival data were collected 
three times a week until no more deaths attributable to the radiation occurred. 
At the conclusion of the experiment, the seed was harvested and weighed. 

In February 1970 a similar experiment using the same treatments as used for 
barley was carried out with hard red spring wheat, Triticum aestivum 'Indus.' 
There were nine exposures of 10 plants each, plus a nonirradiated control for 
each treatment. The plants were transplanted into 4-in. clay pots and placed in a 
light- and temperature-controlled growth room. The light was cool white 



310 BOTTINO AND SPARROW 

fluorescent and supplemental incandescent (approximately 1600 ft-c) on an 
18-hr day, and the temperature was 68 ± 2°F at night and 72 ± 2°F during the 
day. Again survival data were collected three times a week, and the seed was 
collected and weighed at the end of the experiment. 

An experiment to study the effect of exposure rate was conducted with 
germinating seeds of barley, Hordeum vulgare 'Himalaya.' Dry seeds (approxi- 
mately 12% water content) were planted on blotters according to the method of 
Myhill and Konzak. 4 Irradiation began 24 hr after planting and the seeds were 
given an exposure of 1600 R delivered at 32 exposure rates ranging from 60 to 
4800 R/hr for periods ranging from 26.6 hr to 19.8 min. Fortv seedlings per 
exposure-rate treatment were used. After irradiation the seedlings were returned 
to a growth chamber and grown at 80° F under continuous fluorescent light. A 
constant high humidity was maintained in the chamber by bubbling air through 
a water reservoir. The height of the first leaf was measured 8 days after 
irradiation. 



RESULTS 

The results of the lettuce experiment are given in Fig. 3. The survival data 
(Fig. 3a) are shown on a probit plot of survival as percent of control against 
exposure for the three treatments. The graph shows the computer-fitted lines 
and actual data points. No difference was found between the Bu + FDS and the 
FDS treatments. Both treatments were more effective in reducing survival than 
the 16-hr CR treatment. The LD 50 values for the three treatments were 
4.79 ± 0.10 kR for FDS, 4.97 ± 0.12 kR for Bu + FDS, and 7.01 ± 0.12 kR for 
the 16-hr CR. 

The yield data (Fig. 3b) show very little difference between the three 
treatments at the low exposures. At the higher exposures there was no difference 
between the results of the Bu + FDS and FDS treatments, but both were clearly 
more effective in reducing yield than the 16-hr CR treatment. A considerable 
amount of growth stimulation was evident at the lower exposures for all three 
treatments. This was found to be caused by the increased production of axillary 
growth, which contributed to the augmented fresh weight of the plant. 

The survival results for the lettuce CR treatments are compared in Table 1. 
As the exposure time increased, the exposure required to produce the three 
given end points also increased. The nature of this relation is shown for the 
LD 50 values in Fig. 4, where LD 50 is plotted against the log of exposure time. 
There is little change in LD 50 for the 1- and 2-hr treatments. As the exposure 
time is increased, however, LD 50 increases almost with the square of the 
exposure time. 

The results from the barley experiment are shown in Figs. 5 and 6. Figure 5 
shows the probit plot of survival against exposure for the FDS and 16-hr CR 
treatments. The data are somewhat variable because only 10 plants per exposure 



99.9 




311 



Fig. 3 (a) Probit plot of survival as percent of control vs. exposure for lettuce 
given 16-hr CR (•) and 36-hr FDS (■) and Bu + FDS (O) treatments, (b) Mean 
weight per treated plant as percent of control vs. exposure for lettuce for the 
same three treatments. ~[ indicates ± standard deviation (Ref. 2). 



312 



BOTTINO AND SPARROW 



Table 1 

COMPARISON OF THE SURVIVAL END POINTS FOR 
1-, 4-, 8-, AND 16-HR CR TREATMENTS FOR LETTUCE 



1-hr CR, kR ± S.D.* 4-hr CR, kR ± S.D. 8-hr CR, kR ± S.D. 16-hr CR, kR ± S.D. 



LD 10 2.35 ±0.06 

LD 50 2.57 ±0.06 

LD 90 2.78 ±0.08 



3.03 ±0.15 
3.47 ±0.10 
3.90 ±0.12 



4.59 ±0.11 
5.03 ±0.07 
5.46 ±0.1 3 



6.39 ±0.11 
7.01 ±0.07 
7.64 ±0.10 



The abbreviation S.D. is standard deviation. 



it 

6 
in 

Q 



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5 8 10 

EXPOSURE TIME, hr 



20 



Fig. 4 LD50 vs. log of exposure time for lettuce irradiated for 1, 4, 8, and 
16 hr a; constant rates. T indicates ± standard deviation. 



were used, but the results are consistent with those for the other species in 
showing the FDS treatment to be more effective in reducing survival than the 
16-hr CR treatment. The yield data (Fig. 6) resemble the lettuce data (Fig. 3b) 
in that there is little difference between the FDS and 16-hr CR treatments at the 
lower exposures, but at exposures of 4 kR or more the CR treatment is clearly 
less effective in reducing yield. The 16-hr CR values are consistently above the 
FDS values although they are not always significantly different from them. 
Representative plants from the surviving exposures of the three treatments are 
shown in Fig. 7. 

The probit plot of survival for wheat against exposure is given in Fig. 8, and 
again the FDS treatment was more effective in reducing survival than the 16-hr 
CR treatment. The yield data (Fig. 9) are similar to those for lettuce and barley 



EFFECTS OF EXPOSURE TIME AND RATE 



313 




2 3 4 

EXPOSURE, kR 

Fig. 5 Probit plot of survival as percent of control vs. exposure for barley 
given 36-hr FDS and 16-hr CR treatments. 



in that the FDS treatment is more effective in reducing yield than the 16-hr CR 
treatment at the high exposures only. Representative plants of the surviving 
exposures from all treatments are shown in Fig. 10. 

It became clear that a close relation might exist between the effects 
produced by 8-hr CR treatments and 36-hr FDS treatments. Therefore a 
comparison between these two treatments for both survival and yield was made 
for all three crops. This comparison is given for survival in Table 2 and Fig. 11 
and for yield in Figs. 12 to 14. The effects of these two treatments are 
essentially the same, especially at the LD 50 . Table 2 shows that the LD 50 values 
for each crop were not significantly different at the 5% level. The situation is 
comparable when yield is the criterion of effect studied (Figs. 12 to 14). 

The results of the barley exposure-rate experiment are given in Fig. 15. The 
injury increased in proportion to the log of exposure rate between 60 and 



314 



BOTTINO AND SPARROW 




EXPOSURE, kR 

Fig. 6 Log mean weight of seeds per treated plant (in grams) vs. exposure for 
barley given 36-hr FDS and 16-hr CR treatments. T indicates 99% confidence 
interval. 



1000 R/hr. However, very little change in the level of injury was found between 
1000 and 4800 R/hr. 



DISCUSSION 



Most of the results given here may be explained on the basis of exposure 
rate; i.e., for the same total exposure, more damage occurs with high exposure 
rates than with low exposure rates. This, of course, is not a new concept in 
radiobiology, and the literature on the subject is too extensive to be reviewed in 






EFFECTS OF EXPOSURE TIME AND RATE 



315 



FDS 



hr CR 




CONTROL 0.50/ \ 1.00/ \ 1.25 \ 1.50/ \ 1.75 / \ 2.00 



Fig. 7 Representative barley plants from the surviving exposures for 36-hr 
FDS, 8-hr CR, and 16-hr CR treatments. Exposures are given in kiloroentgens. 



316 



BOTTINO AND SPARROW 




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317 




CONTROL 1. 60 



Fig. 10 Representative wheat plants from the surviving exposures of 36-hr 
FDS, 8-hr CR, and 16-hr CR treatments. Exposures are given in kiloroentgens. 



depth here. In the majority of the published work, the effect measured increases 
with increasing exposure rate. This has been found for survival in Solarium, 5 
barley, 6 Neurospora, 1 and aerobic HeLa cells; 8 for growth inhibition in 
Vicia A and barley roots; 1 1 for chromosome aberrations in pea 12 and barley 
seeds; and for mutations in barley 6 and Neurospora. 1 An oxygen requirement 
has been shown for the expression of this exposure-rate effect. 8 ' 14 This need is 
presumably due to the presence of repair mechanisms that require oxygen and 



318 



BOTTINO AND SPARROW 



Table 2 

COMPARISON OF LD 50 VALUES FOR THE 

8-HR CR AND FDS TREATMENTS FOR 

LETTUCE, BARLEY, AND WHEAT 



Crop 


Treatment 


LD 50 , kR± S.D.* 




Lettuce 


FDS 
8-hr CR 


4.79 ±0.05 
5.03 ±0.07 


N.S.t 


Barley 


FDS 

8-hr CR 


1.99 ±0.08 
1.91 ±0.04 


N.S. 


Wheat 


FDS 
8-hr CR 


3.09 ±0.71 
3.45 ± 1.12 


N.S. 



The abbreviation S.D. is standard deviation. 
tThe abbreviation N.S. means not significant at 
the 5% level. 




Barley __ 




Wheat _. 



12 3 4 
EXPOSURE, kR 



Fig. 11 Comparison of probit plots of survival as percent of control vs. 
exposure for lettuce, barley, and wheat given 84nr CR (D) and 36-hr FDS 
treatments (■). 



EFFECTS OF EXPOSURE TIME AND RATE 



319 



200 



100 — 




12 3 4 5 

EXPOSURE, kR 

Fig. 12 Log mean weight per treated plant (in grams) vs. exposure for lettuce 
given 8-hr CR and 36-hr FDS treatments. T indicates 99% confidence interval. 



function most efficiently at low exposure rates. There are some limits to the 
exposure-rate effect, however. At very high exposure rates, further increases in 
rate do not bring about further increases in effect. This is in part a limitation of 
the system, as shown in the work of McCrory and Grun 5 where the 100% 
lethality level imposes an upper limit to the rate effect. This is not to say that an 
additional exposure-rate effect could not be shown, however; if the total 
exposure was decreased, there probably would be an additional exposure-rate 



320 



BOTTINO AND SPARROW 







EXPOSURE, kR 



Fig. 13 Log mean weight of seeds per treated plant (in grams) vs. exposure 
for barley given 8-hr CR and 36-hr FDS treatments. T indicates 99% 
confidence interval. 



EFFECTS OF EXPOSURE TIME AND RATE 



321 



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effect. At the other end of the response curve, where the exposure rate is very 
low, a point is reached where no difference between irradiated and nonirradiated 
plants can be detected. This was observed by Hall and Bedford 1 for growth 
inhibition in Vicia roots and in some studies with chronic irradiation using many 
species. 15-17 This has led to the conclusion that, although the cumulative 
exposure is important, the rate at which that exposure is delivered is a more 
important factor. 1 7 

Thus there is substantial evidence in the literature for the exposure-rate 
effect reported here. We have observed an increasing effect with increasing 
exposure rate and have also reached the point in rate where no additional 
changes in effect occur with increasing rate. Experiments examining the response 
to lower exposure rates are under way. The most important factors controlling 
the specific exposure-rate effect are the species and criterion of effect used, the 
total exposure, and the environmental conditions during and after irradiation. 
Manipulation of these factors, e.g., lowering the total exposure, may allow one 



322 



BOTTINO AND SPARROW 





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50 100 200 500 1000 

EXPOSURE RATE, R/hr 



2000 



5000 



Fig. 15 Seedling height as percent of control vs. log of exposure rate for 
barley seedlings given a total exposure of 1600 R. 



to demonstrate an effect at higher exposure rates since the capacity of the 
system to respond would be greater under conditions more conducive to 
expression of the effect. 

We have reported both here and previously 1 ' 2 that the FDS treatment is 
more effective in reducing survival and yield than the 16-hr CR treatment. The 
ratios of exposures at the LD 50 for 16-hr CR to FDS are 1.43 for lettuce, 1.23 
for barley, and 1.3 7 for wheat; these ratios agree well with the average of 1.4 for 
seven other species previously reported. The constant difference between the 
two treatments which was observed for survival was not observed for yield. At 
exposures up to the region of the FDS LD 50 , little difference between the two 
treatments was observed. Above this exposure the yield for the FDS treatment 
falls off much more rapidly than the yield for the 16-hr CR treatment, and there 
is clearly a difference between the two. This difference in effectiveness is due to 
the very high exposure rates encountered in the early part of the FDS treatment. 
The average exposure rate in roentgens per hour (weighted for the shield 



EFFECTS OF EXPOSURE TIME AND RATE 323 

timings) for a 5000-R exposure was calculated to be 791 R/hr for an FDS 
treatment as compared with 312.5 R/hr for the same total exposure from a 
16-hr CR treatment. Thus the greater effectiveness of the FDS treatment can be 
explained by this difference of about 2.5 times in exposure rate. The fact that 
the survival and yield criteria for the FDS and Bu + FDS treatments are not 
greatly different is due to the use of essentially the same exposure-rate patterns 
for the two types of treatments (see Fig. 1). 

The barley-seedling-height experiment shows that radiation damage increases 
with increasing exposure rate at rates below 1000 R/hr and provides additional 
support for our conclusion that the greater effectiveness of the FDS treatment is 
due to the initial high exposure rates. About 40% of the total exposure of 
5000 R, which was lethal for lettuce, wheat, and barley, was given at 1300 R/hr. 
Although the criterion of effect studied was seedling-height reduction, it can be 
assumed that the survival and grain yield would also respond in a similar manner 
to variations in exposure rate. Thus the high overall exposure rate would be 
more than adequate to explain the increased effectiveness of the FDS treatment. 

The similarity in effect between the 8-hr CR treatment and the FDS 
treatment is interesting from a practical standpoint. The exposure rates for the 
two treatments, compared for a 5000-R exposure, were found to be 625 R/hr 
for the 8-hr CR exposure and 791 R/hr for the FDS exposure. On this basis we 
would predict a similar level of effect for the two treatments if exposure rate 
played an important role in determining the level of damage. This finding is 
important sinc'e it implies that laboratories lacking the facilities to simulate 
fallout decay may obtain similar results by using 8-hr CR treatments. Although 
the 8-hr CR wheat data deviate somewhat from the FDS data for survival, the 
similarity between the FDS and the 8-hr CR data for all crops is very good, and 
relevant data on survival and yield for other crops can be made by using 8-hr CR 
treatments. 

ACKNOWLEDGMENTS 

We wish to thank Brenda Floyd, Susan S. Schwemmer, E. E. Klug, Leanne 
Puglielli, J. Newby, R. Sautkulis, Pamela Silimpen, and J. Bryant for assistance 
with the irradiations and data collection; R. A. Nilan for supplying the barley 
seed; and C. F. Konzak for supplying the wheat seed. The assistance of K. H. 
Thompson with statistics and Virginia Pond and Susan S. Schwemmer with 
critical comments on the manuscript is also acknowledged. 

This research was carried out at Brookhaven National Laboratory under the 
auspices of the U. S. Atomic Energy Commission and the Office of Civil 
Defense, Department of the Army, Washington, D. C, under Project Order No. 
DAHC20-69-C 0167, Work Unit 3133E. Contracting office technical representa- 
tive was D. W. Bensen. This report has been reviewed and approved for 
publication by the Office of Civil Defense. Approval does not signify that the 
contents necessarily reflect the views and policies of the Office of Civil Defense. 



324 BOTTINO AND SPARROW 

REFERENCES 

1. A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on 
Growth and Yield of Cabbage, Maize, Peas and Radish, Radiat. Bot., 9: 77-92 (1969). 

2. A. H. Sparrow, Brenda Floyd, and P. J. Bottino, Effects of Simulated Radioactive 
Fallout Buildup and Decay on Survival and Yield of Lettuce, Maize, Radish, Squash, and 
Tomato, Radiat. Bot., 10: 445-455 (1970). 

3. G. M. Clark, F. Cheng, R. M. Roy, VV. P. Sweaney. W. R. Bunting, and D. G. Baker, 
Effects of Thermal Stress and Simulated Fallout on Conifer Seeds, Radiat. Bot., 1 -. 
167-175 (1967). 

4. R. R. Myhill and C. F. Konzak, A New Technique for Culturing and Measuring Barley 
Seeds, Crop Sci, 7 ': 275-276 (1967). 

5. J. McCrory and P. Grun, Relationship Between Radiation Dose Rate and Lethality of 
Diploid Clones of Solarium, Radiat. Bot., 9: 27-32 (1969). 

6. A. Silvy and P. Pereau-Leroy, Effets genetiques d'irradiations gamma de courte duree et 
a differents debits de dose sur des plants d'orge (var. Piroline) en cours de 
developpement, in Induced Mutations in Plants, Symposium Proceedings, Pullman, 
Wash., 1969, pp. 181 — 193, International Atomic Energy Agency, Vienna, 1969 
(STI/PUB/231). 

7. F. J. de Serres, H. V. Mailing, and B. B. Webber, Dose-Rate Effects on Inactivation and 
Mutation Induction in Neurospora crassa, in Recovery and Repair Mechanisms in 
Radiobiology, Brookhaven Symposia in Biology Number 20, June 5 — 7, 1967, Upton, 
N. Y., USAEC Report BNL-50058, pp. 56-76, Brookhaven National Laboratory. 

8. E. J. Hall, J. S. Bedford, and R. Oliver, Extreme Hypoxia-, Its Effect on the Survival of 
Mammalian Cells Irradiated at High and Low Dose Rates, Brit. J. Radiol., 39: 302—307 
(1966). 

9. E. J. Hall and J. Cavanagh, The Oxygen Effect for Acute and Protracted Radiation 
Exposures Measured with Seedlings of Vicia faba, Brit. J. Radiol, 40: 128-133 (1967). 

10. E. J. Hall and J. S. Bedford, A Comparison of the Effect of Acute and Protracted 

Gamma Radiation on the Growth of Seedlings of Vicia faba. Part 1. Experimental 

Observations, Int. J. Radiat. Biol, 8: 467-474 (1964). 
ILL. Cercek, M. Ebert, and D. Greene, RBE, OER, and Dose-Rate Effects with 14 MeV 

Neutrons Relative to 300 kVp X-Rays in Barley Roots, Int. J. Radiat. Biol, 14: 

453-462 (1969). 

12. A. M. Akopyan, Effect of Different Types of Ionizing Radiations in Peas. II. Dose and 
Dose Rate Effects on the Frequency of Chromosomal Aberrations of Pea Seeds After 
Gamma Irradiation, Genetika, 7 •. 34—38 (1967). 

13. K. A. Filev, Postirradiation Seed-Storage Effect as Related to Irradiation Dose and Rate, 
Dokl Akad. Nauk SSSR, 169: 680-682 (1966). 

14. D. L. Dewey, An Oxygen Dependent X-Ray Dose-Rate Effect in Serratia marcescens, 
Radiat. Res., 38: 467-474 (1969). 

15. J. M. Bostrack and A. H. Sparrow, The Radiosensitivity of Gymnosperms. II. On the 
Nature of Radiation Injury and Cause of Death of Pinus rigida and P. strobus After 
Chronic Gamma Irradiation, Radiat. Bot., 10: 131-143 (1970). 

16. G. M. Woodwell and A. H. Sparrow, Predicted and Observed Effects of Chronic Gamma 
Radiation on a Near-Climax Forest Ecosystem, Radiat. Bot., 3: 231 — 237 (1963). 

17. J. E. Gunckel, A. H. Sparrow, Ilene B. Morrow, and Eric Christensen, Vegetative and 
Floral Morphology of Irradiated and Non-Irradiated Plants of Tradescantia paludosa, 
Amer. J. Bot., 40: 317-332 (1953). 



DOSE-FRACTIONATION STUDIES 

AND RADIATION-INDUCED PROTECTION 

PHENOMENA IN AFRICAN VIOLET 



C. BROERTJES 

Institute for Atomic Sciences in Agriculture, Wageningen, The Netherlands 



ABSTRACT 

Leaves of African violet, which develop adventitious buds on petioles after rooting, have 
been used as test material for dose-fractionation studies with X rays and fast neutrons. The 
parameters used were survival of the leaves, production of adventitious plantlets per leaf, 
and mutation frequency. 

The aim of the experiments was to determine the relation between initial dose, time 
interval, and the extent of the radioinduced protection. The "optimal" initial dose inducing 
maximal protection (equivalent to approximately 3 krads) proved to be 500 rads of X rays 
and fast neutrons at an "optimal" time interval of 8 to 12 hr. 

Repeated irradiations with the optimal initial dose at 8-hr time intervals induce a 
protection much higher than that of a single pretreatment, reaching a maximum after 
approximately 10 irradiations. 

No qualitative differences were found between X rays and fast neutrons. The relative 
biological effectiveness (RBE) for protection is found to be 1, whereas the RBE for acute 
irradiations is 2. 

The results presented are discussed and compared with literature data dealing mainly 
with mammals. A few questions arise about the significance of the phenomena described in 
relation to radiotherapeutic procedures. 



African violet, Saintpaulia ionantha 'Utrecht', was used to study the effects of 
acute and chronic irradiation with X rays and fast neutrons. During these 
experiments a very pronounced dose-rate effect was observed. 1 Dose- 
fractionation experiments were carried out in an attempt to analyze the 
mechanisms involved; again both X rays and fast neutrons were used. The 
experiments described here were carried out to determine the interaction 
between various initial doses, time intervals, and repeated irradiations and the 
radiosensitivity of the material. 

The results are discussed in terms of radioinduced protection or improved 
radioinduced repair mechanism. It is impossible to decide which term should be 

325 



326 BROERTJES 

used without knowing exactly the mechanisms involved; protection implies 
prevention of part of the damage by the radiation, whereas improved repair 
speaks for itself. 

The word "protection"' was chosen mainly to emphasize the difference 
between the normal repair that takes place after acute irradiation and the 
phenomena described, which occur after fractionated treatments. 

The explanation of these phenomena is not a simple one. Many authors have 
presented possible explanations, but so far none is completely satisfactory. 
These investigations do not include a study of the mechanisms involved but are 
concerned with more-practical mutation breeding and consequently do not 
contribute to an explanation of the protection phenomena observed. 

MATERIAL, PARAMETERS, AND IRRADIATION FACILITIES 

Material 

African violet, which belongs to the Gesneriaceae, was selected as an 
experimental plant for various reasons. It forms medium-size plants that can be 
grown without difficulties under proper greenhouse conditions throughout the 
year. The species reproduces easily from leaf cuttings, which, after rooting, 
produce 10 to 20 plantlets per leaf from adventitious buds formed at the base of 
the petiole. These adventitious plantlets can be separated from the mother leaf, 
transplanted in boxes or pots, and grown to maturity. 

This reproduction system, the so-called adventitious bud technique, was 
chosen for one important reason: Every adventitious plantlet ultimately 
originates from only one epidermal cell; this results in solid, nonchimeral 
mutants if this cell carries a mutation. After any mutagenic treatment, whether 
short (minutes) or very long (up to 4 weeks), the lower 5 mm of the petiole, the 
region where the adventitious buds are formed, was cut off. In this way it was 
ascertained that the epidermal cells situated higher up the petiole, which had 
undergone the whole treatment as nondhiding, resting cells, were stimulated to 
develop the adventitious buds. This procedure avoided the consequences arising 
from differences in radiosensitivity caused by different cell-division stages as well 
as the chimera formation resulting from mutation induction in the developing 
multicellular meristems during a prolonged treatment (longer than 3 to 5 days). 
In general, 20 leaves per treatment were used. 

Parameters 

Three parameters were used to measure the effect of the irradiation: 

1. Survival of the irradiated leaves (in percent of the control). Only leaves 
that produced at least one plantlet were considered to be alive. 

2. Production of plantlets (average number per leaf in percent of the 
control). This is the most reliable parameter and generally reacts very sharply 



DOSE-FRACTIONATION STUDIES 327 

depending on the intensity of the treatment. Untreated leaves produce 
approximately 15 plantlets per leaf. 

Survival and production were determined 4 to 5 months after planting 
during separation of the plantlets from the mother leaf. 

3. Mutation frequency. This was determined approximately 3 months after 
the separation when the plants were large enough for variations in size, form, 
habit, and color of leaf and plant to be distinguished. This is the least reliable 
parameter since habit, size, and other visible characteristics vary with differences 
in climatic and other conditions and, in addition, are influenced by the previous 
treatments. The decision to consider a plant a mutant was often an arbitrary 
one. 

Irradiation Facilities 

X rays were applied with a Philips 250/25 deep-therapy apparatus, usually 
operating at 250 kV and 15 mA without an additional filter. The dose rate 
applied was always 200 rads/min. Temperature was the only climatic condition 
controlled during irradiation. 

Fast-neutron irradiations were carried out in the sub-core irradiation room of 
the Biological Agricultural Reactor Netherlands (BARN). When the facility was 
operating at full power, a dose rate of 1000 rads/hr in H 2 was obtained in the 
irradiation position. Since Saintpaulia leaves contain 97 to 98% H 2 0, this may 
be considered as the dose rate in the material. 

The fast-neutron spectrum is similar to a fission spectrum and has an average 
energy of approximately 2 MeV. The gamma contamination amounts to 80 
rads/hr (Ref. 2). 

RESULTS 

In this discussion of the results of the dose-fractionation experiments, I will 
refer often to the acute-dose-effect curves. As can be seen in Figs. 1 and 2, the 
form of the curves is almost identical for X rays and fast neutrons. The only 
difference is that on a rad basis fast neutrons from the BARN reactor have a 
relative biological effectiveness (RBE) for the three parameters used of 
approximately 2 compared with the X rays. The results presented here indicate 
that both radiations are qualitatively alike. 

The first experiment, in which two equal semilethal doses (50% of the 
sublethal X ray dose of 6 krads) were applied at various time intervals, clearly 
showed that after an interval of more than 8 to 12 hr the effect of the two 
fractions was identical with the effect of only one fraction for both survival 
(Fig. 3) and production (Fig. 4). It can be seen, especially from Fig. 4, that the 
first dose must have induced some kind of change resulting in a mechanism that 
develops in time, reaches a maximum after approximately 12 hr, and gradually 
breaks down in the following days; it was still noticeable, however, after 120 hr. 



328 



BROERTJES 



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\ \ • 








h- 










v \ 








z 


HO 








\ \ 




A 


— 


n 










1 s \ 








CJ 










+ N ^ \ 








u_ 

c 










t\\ 


A ... 


•'"*" 




S5 


40 








A •> 


V ' 




" 




20 

n 


A 


A 


.. 


A '^ - 

A .'"''a Mutation 
..•"'A 

1 1 






- 



DOSE, krads 

Fig. 2 Dose-effect curves after acute fast-neutron treatments (1000 rads/hr) 
of African violet leaves. 



DOSE-FRACTIONATION STUDIES 



329 



100 


i i J J J 


c 




• 


• 












80 


- > 
















— 


60 


I 

1 














, 3 krads acute 


— 


40 


-- 


,6 krads acute 


20 


► 
















— 


n 


1 I 1 1 1 



48 96 

TIME INTERVAL, hr 



144 



Fig. 3 Effect on survival of two semilethal X-ray doses (3 krads) given at 
various time intervals. 





I 


i 


i 


i i 




100 


• 












f^~ 


• 








80 


/ • 








— 


60 


— / * 
/ • 






• N^ 


— 


40 


7 






,3 krads acute 


— 






,6 krads acute 


20 












n 


• 

i 


i 


i 


1 1 



48 96 

TIME INTERVAL, hr 



144 



Fig. 4 Effect on production of two semilethal X-ray doses (3 krads) given at 
various time intervals. 



330 BROERTJES 

As mentioned previously, it was decided to use the word "protection 1 ' for this 
mechanism. 

Various questions arise: (1) Can an optimal initial dose be determined which 
induces a maximal protective effect in the leaves? (2) What is the relation 
between protection and the time interval separating the initial dose and the 
second dose? (3) What is the extent of the protection? And (4) What is the 
effect of repeated irradiation with the optimal initial dose at the optimal time 
interval. 

Initial Dose 

Various initial doses have been applied, ranging from very small ones (1-, 10-, 
30-, 75-, and 150-rad X-ray doses and comparable doses of fast neutrons) up to 
the semilethal X-ray dose of 3 krads. These were followed, after the optimal 
time interval (8 hr, see the following section), by a series of second doses, i.e., 
the semilethal X-ray dose of 3 krads, the sublethal dose of 6 krads and a number 
of lethal doses (7, 8, 9, and 10 krads) and comparable fast-neutron doses. The 
high second doses were given to test the extent of the protection. 

As can be seen in Figs. 5 and 6 (survival and production, respectively, after 
various initial doses of X rays or fast neutrons), a very pronounced protective 
effect is initiated by a first dose of 500 to 1000 rads of X rays or fast neutrons. 
The exact optimum is hard to define since a fairly large dose range, covering a 
few hundred rads, induces almost maximal protection. Moreover the optimum 
depends on the extent of the second dose. A larger second dose requires a larger 
initial dose for maximal protection; this indicates a small increase in protection 
with increasing initial dose in the dose range mentioned. 

To define the optimal initial dose, we must take into account the 
nonrepaired effects of the initial dose. They mask the effect of the protection, 
especially when higher initial doses are applied, because their contribution to the 
total effect increases with dose. The choice of the optimal initial dose has 
therefore fallen on an initial dose in the lower region of the dose range inducing 
nearly maximal protection, i.e., 500 rads of X rays or fast neutrons. 

Unfortunately some preliminary experimental results suggested that 170 rads 
of fast neutrons was the optimal initial dose in African \iolet. This means that a 
few experiments were carried out with repeated irradiations with fast neutrons 
at a suboptimal initial dose; these cannot be directly compared with the repeated 
X-ray irradiation using the optimal initial dose (see the section on repeated 
irradiation). 

Time Interval 

The initial dose, selected to study the effect of time interval (500 rads of 
X rays or 170 rads of fast neutrons), was separated from the second dose 
(generally 3 krads of X rays or 1700 rads of fast neutrons and 6 krads of X rays 



DOSE-FRACTIONATION STUDIES 



331 



100 — 



80 — 



60 



40 



20 



I 






1 






f^ • '^^'^^ 




.^ 








/ • 






s — ^« 


• 




/ ^ 












/ N 












-/ ' \ 












/ \ 










— 


- i \ 










— 


i \ 












4 ' \, 












.J il 


A 




1 







12 2 

INITIAL DOSE, krads 

Fig. 5 Effect of various initial doses on survival. Second doses were 6-krad 

X rays ( — ) and 3.3-krad fast neutrons ( ); there was an 8-hr time interval 

between first and second doses. 



100 




1 2 3 

INITIAL DOSE, krads 

Fig. 6 Effect of various initial doses on production. Second doses were 5-krad 

X rays ( — ) and 2. 5-krad fast neutrons ( ); there was an 8-hr time interval 

between first and second doses. 



332 



BROERTJES 



or 3400 rads of fast neutrons) by time intervals ranging from 1 to 12 hr and 
from 24 to 240 hr. 

As is shown in Figs. 7 and 8, a protective mechanism builds up very rapidly, 
reaching its maximum after 8 to 12 hours and gradually decreasing with 
increasing time interval. After approximately 120 hr the protective effect has 
disappeared almost completely regardless of the type of radiation used. 




24 



72 120 

TIME INTERVAL, hr 



168 



Fig. 7 Effect of various time intervals on survival and production at an initial 
X-ray dose of 500 rads and a second X-ray dose of 6 krads. At 6 krads there is 
approximately 10% survival and approximately 20% production-, an X-ray dose 
of 6.5 krads is lethal. 



In relation to the repeated irradiations planned, the optimal time interval 
was defined as the shortest time needed for maximal protection. The selected 
time interval of 8 hr permitted 60 repeated irradiations of the material with the 
optimal initial dose within 20 days. A time interval of 12 hr would have 
extended the experiment to 30 days, which is too long for the separated leaves 
to remain in sealed plastic bags. 

Extent of Protection 

A series of high second doses, most of which are lethal when given as an 
acute single dose, were applied to test the extent of the radioinduced protection. 
As can be seen in Fig. 9, even after an X-ray dose of 9 or 10 krads, or 
comparable fast neutron doses, on the basis of an RBE of 2.0, there is a surviving 
fraction corresponding to an acute single dose approximately 3 krads lower. In 
other words, a low initial dose of 500 rads induces a protective mechanism with 
an extent of approximately 3 krads. 






DOSE-FRACTIONATION STUDIES 



333 




TIME INTERVAL, hr 

Fig. 8 Effect of various time intervals on survival and production at an initial 
fast-neutron dose of 170 rads and a second fast-neutron dose of 3.4 krads; 
fast-neutron doses of 3.3 and 3.5 krads are lethal. 



100 



BO- 



'S 60 — 



40 — 



20 — 





1 


. L x k i 


XV 


I 


— 




*^*0 * ^— « 

V\ V 

\ \ N 

\ \ 

Acute \ \ 
fast \ \ 






neutron s\ \ 






— 




\ \ A 

\ \ Acute 
v \X rays 




— 


— 


I 


\ \ 
\ \ 
\ \ 
\ \ 


s»l I 


1 ^ 



5 6 7 

X RAYS 

I 



10 



FAST NEUTRONS 
SECOND DOSE, krads 



Fig. 9 Extent of protection induced by an initial X-ray dose of 600 rads 
(— • — ) or an initial fast-neutron dose of 500 rads (--A--), tested by 
applying various second doses of X rays or fast neutrons after an 8-hr interval. 



334 



BROERTJES 



This is also very clearly demonstrated by an experiment in which an optimal 
initial X-ray dose (500 rads) or the suboptimal fast-neutron dose of 170 rads 
preceded a series of second doses of either fast neutrons or X rays by an 8-hr 
time interval. The distance between the acute lines and the other, parallel, lines 
is approximately 3 krads, as is shown in Figs. 10 and 11, again on the basis of an 
RBE of 2.0. 



100 



80 — 



o 60 





I 


I L I . 


I I I 







v,^ 






V 










Acute 
fast 


\ \ \\ \ 
\ \ V \ 









neutrons \ \ \\ 


i \ 









M \ 


\ \ 








M \ 


* \ 








\ \ \ 
\\ 


. \ \ 

\ \ \ 
\ \ \ 














\ \ Acute 


\ N \ 








MX rays 
\\ 








I 


I NV 


\i ---» r 





40 



20 — 



4 6 8 10 

X RAYS 



12 



14 



12 3 4 5 6 7 

FAST NEUTRONS 
SECOND DOSE, krads 

Fig. 10 Effect on survival of the optimal initial dose (500 rads of X rays or 
170 rads of fast neutrons) after various second doses of X rays or fast 
neutrons. —A*-, both initial and second doses of X rays-, — A — , initial dose of 
X rays, second dose of fast neutrons; --■--, both initial and second doses of 
fast neutrons; and - - □- -, initial dose of fast neutrons, second dose of X rays. 



Repeated Irradiation 

To investigate whether repeated irradiation with the optimal initial dose at 
optimal time intervals would result in increased, decreased, or equal protection, 
we applied 500-rad X-ray or 170-rad fast-neutron doses repeatedly at 8-hr 
intervals. During the treatment the leaves were sealed in plastic bags and kept in 
the dark except during handling and irradiation. The temperature was kept at 
approximately 20°C. After 1, 5, 10, 15, etc., to 60 repetitions, a series of higher 
doses was applied to test the protection, i.e., X-ray doses of 1.5, 3, 4.5, 6, 8, and 
10 krads or fast-neutron doses of 0.8, 1.7, 2.5, 3.4, 5, and 6.8 krads. 



DOSE-FRACTIONATION STUDIES 



335 





1^-0^1 1 


i 


i 


00 


^v\ \ 

\ \\ \\ \ 






80 


A \ \ \ 

A \\ \ 






60 









\\ x \\ \ 








\ \ \ \\ \ 








Acute fast neutrons\ \ ^ \ 

\\ Acute ▼S.X 






40 




— 




\\ v \\A 








x . \ X rays ^ « 






20 


\\ 


\A 


_ 




n i 


A \ V 






i i i v i 


\v^- 




n 


1 IV. 1 







X RAYS 

L 



12 



14 



12 3 4 5 6 7 

FAST NEUTRONS 

SECOND DOSE, krads 

Fig. 11 Effect on production of the optimal initial dose (500 rads of X rays 
or 170 rads of fast neutrons) after various second doses of X rays or fast 
neutrons. — A — , both initial and second doses of X rays-, — ▲ _ ) initial dose of 
X rays, second dose of fast neutrons; --■--, both initial and second doses of 
fast neutrons; --□--, initial dose of fast neutrons, second dose of X rays. 



As can be seen in Figs. 12 and 13, which are based on the same data but are 
presented differently (i.e., survival at an initial X-ray dose of 500 rads), the 
protection increases drastically with the number of repetitions. After from 5 to 
60 repetitions, all high doses applied (including 10-krad X-ray doses) result in 
100% survival. 

Similar results are obtained with fast neutrons (Figs. 14 and 15); these data 
also show clearly that the protection reaches a maximum after 5 to 15 
repetitions and then decreases fairly rapidly. This can also be seen in Fig. 16, in 
which the values of Fig. 15 are corrected for accumulated unrepaired damage of 
the repeated irradiations as well as for storage. (Storage for 3 weeks causes a 
decrease in survival and production.) 

When the results obtained after repeated exposures are compared with those 
after a single pretreatment, it is obvious that the extent of the protection 
increases considerably after a few irradiations at the optimal initial dose and 
reaches a value that is much higher than the best single pretreatment. For 



336 



BROERTJES 



100 


\__ 


__ I i_ 


-; 


t 


80 








— 


60 








— 


40 




Acute\ 




• 


20 

n 


I 


i N 




I I \ 



2 4 6 8 10 

LAST DOSE (X RAYS), krads 

Fig. 12 Effect on survival of repeated X irradiations of 500 rads at 8-hr 
intervals; various last doses of X rays were applied. ...•..., one pretreatment 
with 500 rads; , 5 to 60 repetitions. 





I I 6 krads I I ! 


100 - 


-^.-r.rrrrn-.-n^- - - - R -- 

/ : 




80- 
I 




— 


60 ■ 


.' 10 krads 


— 


i 

40 I 
I 




— 


I 

2 o j: 







: 






0- 


I I I I 


I I 



10 



20 30 40 

NUMBER OF REPETITIONS 



50 



60 



Fig. 13 Effect on survival of repeated X irradiations of 500 rads at 8-hr 
intervals; various last doses of X rays were applied. 



DOSE-FRACTIONATION STUDIES 



337 



no 


1 . 


1 




1 




1 


1 1 

— k *^-=r A — 


1 

— D D- 
















\ ^ - 


















\ 


















\ 




80 








• \ 






\ 
\ 
\ 




60 


-' / 

/ / 

/ / 










• 


\ 

\ 
\ 




40 


-/ / 
/ / 

/ / 

■i / 












\ 
\ 
\ 
\ • \ 




70 












\ A \ a 



















\ 

























■4 — o-^= 


o 

■T 


— o — 


— o 

1 




1 


\ 1 


1 



10 



20 30 40 50 

NUMBER OF REPETITIONS 



60 



Fig. 14 Effect on survival of repeated fast-neutron irradiations of 170 rads at 
8-hr intervals. Last doses of fast neutrons were 6.7 krads (- - O - -), 5 krads 
(- •-), 3.4 krads (--A--), 1.7 krads (- A -), and 170 rads (-- D - -). 



125 


I I 




1 1 1 1 


100 


.rr*""° ^^\^d 

A ^^ >A. 


D 


-°^ — 




A ^\A 








A ^^ 




-»» 








■»■>. 


75 


— s *^ 




\ A °^ D 




Y ^< 






/ ^ 




A ^^ A 






\ 


^*^v^ D 




/ 


"N. 






A 


-N. >v 


50 


— / 




""*- ^^ » 




/ y^ \ 




\ ^v. 






. \ \. 




1 */• • 




A \ ^v^ 






• ^ ^*- 


25 


t / o 




"\. • r^ 




1 / ^~o 


• 












/ •— ■" 1 




^N^ ! 


n 


o4_^o^-l o 1 — 




1 \- 1 1 



10 



20 30 40 

NUMBER OF REPETITIONS 



50 



60 



Fig. 15 Effect on production of repeated fast-neutron irradiations of 170 
rads at 8-hr intervals. Last doses of fast neutrons were 6.7 krads (--O--), 
5 krads (- •-), 3.4 krads (--A--), 1.7 krads (- A-),and 170 rads (- - □--). 



338 



BROERTJES 





. I 


1 






1 


I 






I 




100 


1 • 


. • 


















80 


/ / 




• 




• " 


N. • 












60 


7 ' 

/ / 


^ 


\ 




• >v 


• 








— 






-o. 


^x^ 














/ 








^ o 














-/ 


A 






s. 












40 








\ 















1 / i 








\ 










• 




A' 


\ 




A 




\ 








20 










\. A 






o 


^> 


Ss <? < 




* • . 






\ 














1 1 • 


*•*. 






\ 














.LJ. — L_ 


1 






1 \ 








1 







A L 




1*— 


1 


l^A- 






1 





30 40 

NUMBER OF REPETITIONS 



50 



60 



Fig. 16 Effect on production of repeated fast-neutron irradiations of 170 
rads at 8-hr intervals; various last doses of fast neutrons were applied; and 

corrections for pretreatment and storage were made. — , 2.5 krads; , 3.4 

krads; , 5*krads; and • • • \ 6.7 krads. 



example, a fast-neutron dose of 5 krads applied after 15 repetitions of 170 rads 
of fast neutrons gives a survival rate of approximately 90% (Fig. 14), whereas 
5 krads after the optimal initial fast-neutron dose of 500 rads is just about lethal 
(Fig. 9). For an initial X-ray dose of 10 krads, these figures are 100 and 0%, 
respectively (Figs. 13 and 9). 

From these figures it would appear that fast neutrons are less effective in the 
induction of protection than are X rays. But it should be borne in mind that the 
repeated fast-neutron irradiations were carried out at the suboptimal initial dose 
of 170 rads. Moreover, the results presented in Figs. 10 and 11 counteract this 
impression, especially when the suboptimal 170-rad fast-neutron line is replaced 
by the optimal 500-rad fast-neutron line of Fig. 9. 



DISCUSSION 



Comparison of X Rays and Fast Neutrons 

As mentioned previously, no fundamental difference in action of X rays and 
fast neutrons from the BARN reactor is evident. It is known that 14-MeV 
neutrons have a much more pronounced direct effect and consequently do not 
show much dose-rate effect when compared with neutrons having an average 
energy of 2 MeV. This is demonstrated very clearly in Figs. 10 and 11, which 



DOSE-FRACTIONATION STUDIES 339 

present the results of an experiment in which a pretreatment of X rays or fast 
neutrons was followed by second doses of X rays or fast neutrons after an 8-hr 
time interval. 

From the experimental results it appears that the optimal initial dose for 
protection is 500 rads of X rays or fast neutrons. Thus the RBE for protection 
isl, but, for survival and production [after both acute and fractionated 
exposures (Figs. 1 and 2 and 10 and 11, respectively)], the RBE has been found 
to be 2. No explanation of this interesting result can be given at the moment. 



( 



Radiation-Induced Protection 

Most literature on this subject deals with microorganisms (Saccharomyces), 
with mammalian cells in vitro, or with animals (chickens, dogs, goats, mice, 
monkeys, pigs, rabbits, rats, and sheep). Generally, whole animals are used to 
study the effect of one or more pretreatments (initial dose, primary dose, 
conditioning dose) prior to a second total-body (mass) irradiation after various 
time intervals. Survival or mortality is generally the parameter used, as for 
example, by Christian et al. 3 for the chicken. Some experimenters irradiated only 
part of an animal; e.g., Bewley et al. 4 irradiated the skin of pigs and used skin 
reactions as a parameter. Others used repopulation as the parameter, as, for 
example, in the mice studies of Denekamp et al. 5 

A number of authors have tried to review all the data on radioinduced 
protection and to classify the many different and often confusing observations 
obtained by various scientists. 6- Krokowski 1 ° standardized the results, 
compared the LD 50 's of the radiation effects with and without preirradiation, 
and put them in a three-dimensional coordinate system. 

We can draw a number of general conclusions from all these data: 

1. Preirradiation induces a protective mechanism. 

2. This protection depends on the intensity of the initial dose, the optimal 
being approximately 10 to 20% of the LD 5 . 

3. The protection also depends on the time interval between first and second 
doses. Generally, an interval of 10 to 14 days is required for optimal protection. 
The protection can last several weeks or even months. 

4. A repeated preirradiation is less effective than a single initial irradiation. 

Krokowski 10 reported the peculiar and interesting fact that radioinduced 
protection can be transmitted by injecting the serum from preirradiated animals 
into nonirradiated animals. The injected animals showed a striking increase in 
radioresistance. 

In plants most dose-fractionation investigations have dealt with the 
phenomenon of chromosome aberrations. Davies, 1 l working with white clover, 
found that, depending on the temperature, protection could be induced by a low 
initial dose built up rapidly at 25°C and reaching a maximum after approxi- 
mately 8 hr. At a lower temperature the protection did not decrease even after 



340 BROERTJES 

4 days. Furthermore, the protection was also dependent on the presence of 
oxygen; in nitrogen no protection was obtained. 

The data presented here agree in part with those in the literature. The 
optimal initial dose mentioned in the literature is approximately 15% of the 
LD 50 , and the extent of the protection induced (increase in tolerance with 
about 1.7) seems to fit fairly well with the data presented here. In contradiction, 
however, is the fact that the protection is reported to stay active in animals over 
an extremely long period whereas in the African violet most of the protective 
effect has disappeared after 5 days. Also in contradiction is the fact that in 
animals a single preirradiation induces a better protection than repeated 
preirradiations. The data presented here clearly demonstrate an optimal 
protection after a 10- to 20-fold repetition of the preirradiation dose. 

A last point to consider is the fact that a 25-fold irradiation with 200-rad 
X rays is often used in radiotherapy; 200 rads is approximately 5 to 7% of the 
lethal dose for mammalian cells and is comparable to the optimal initial dose for 
African violet (500 rads of X rays), which is also approximately 5 to 7% of the 
lethal dose. A 10- to 25-fold irradiation at this dose induces in African violet a 
maximal protective effect. This raises the question of whether a similar reaction 
can be demonstrated in animal tissue. If so, the next question is whether the 
reaction of normal cells is different from, for instance, that of tumor cells. If, 
again, this is the case, one wonders whether this could be of importance for 
radiotherapy in man, realizing, of course, that it is unrealistic to compare 
African violet with man in view of the differences in tissue, cell type, chemical 
composition, chromosome size, and oxygenation, to mention but a few. 

Mutation Frequency 

The original aim of the experiments on the effect of acute, chronic, and 
fractionation experiments in Saintpaulia was to investigate whether a more 
efficient mutagenic treatment could be developed. Radiation has a very complex 
effect on living matter. The energy dissipated in the cells through ionizations is 
the starting point of a number of chain reactions that interfere with all kinds of 
metabolic and other processes and ultimately result in permanent physiological 
and genetic effects, in spite of the generally large repair capacity of the cells of 
the organism involved. 

The physiological effect, for instance, expressed in survival percentage of the 
irradiated plant parts, obviously depends on a great number of factors, e.g., the 
radiosensitivity of the plant species, the total dose, the dose rate, the type of 
radiation, and climatic and other environmental conditions before, during, and 
after the treatment. 

This is also the case with the genetic effect, expressed in mutation 
frequency, for instance, although the role of environmental conditions is much 
less obvious and for the greater part unknown. It would be of great importance 
for the practical plant breeder to have available clear-cut data on the optimal 



DOSE-FRACTIONATION STUDIES 341 

method of irradiation which induces the highest possible frequency of useful 
mutants. Since repair of physiological and genetic effects a priori may be the 
result of partly different processes, it must be possible to separate the two by a 
proper treatment in such a way that the physiological damage to survival, 
growth, and fertility as well as the undesirable part of the genetic effect 
(chromosome aberrations) is minimal, whereas the desired genetic effect (gene 
mutations, favorable chromosome rearrangements, etc.) is maximal. 

The effect of various factors on mutation frequency is mentioned here only 
very incidentally for various reasons. First, the parameter itself is not so reliable 
as the two physiological parameters of survival and production. Second, the 
calculations are not advanced enough at the present time to give a clear-cut 
picture. Third, such a discussion actually belongs in an article dealing with 
mutation breeding. 

At the moment we can only say that an initial dose also protects against the 
genetic effect of a second irradiation or series of irradiations, but the protection 
is not so pronounced as in survival and production. By using these facts, we 
could obtain a greater number of mutants from a given number of irradiated 
leaves. This idea will be worked out in greater detail as soon as all data are 
available. 



ACKNOWLEDGMENTS 

I wish to thank my colleagues for their contributions in the form of positive 
discussions. Miss E. van Balen deserves special thanks for her efforts in the 
mathematical treatment of 10 years' accumulation of data as well as for the large 
number of figures that had to be made. 



REFERENCES 

1. C. Broertjes, Dose-Rate Effects in Saintpaulia, in Mutations in Plant Breeding II, Panel 
Proceedings, Vienna, 1967, pp. 63—71, International Atomic Energy Agency, Vienna, 
1968 (STI/PUB/182). 

2. K. H. Chadwick and W. F. Oosterheert, Neutron Spectrometry and Dosimetry in the 
Subcore Facility of a Swimming Pool Reactor, At ompraxis, 15: 178 — 180 (1969). 

3. E. J. B. Christian et al., Mechanisms of 7-Ray Induced Radioresistance to Early 
Mortality in the 3-Day Chick, Radiat. Res., 25: 179 (1965). 

4. D. K. Bewley, S. B. Field, R. L. Morgan, B. C. Page, and C. J. Parnell, The Response of 
Pig Skin to Fractionated Treatments with Fast Neutrons and X Rays, Brit. J. Radiol, 
40(478): 765-770 (1967). 

5. J. Denekamp, J. F. Fowler, K. Kragt, C. J. Parnell, and S. B. Field, Recovery and 
Repopulation in Mouse Skin After Irradiation with Cyclotron Neutrons as Compared 
with 250-kV X rays or 15-MeV Electrons, Radiat. Res., 29: 71-84 (1966). 

6. M. P. Dacquisto, Acquired Radioresistance. A Review of the Literature and Report of a 
Confirmatory Experiment, Radiat. Res., 10: 118-129 (1959). 



342 



BROERTJES 



7. J. Maisin, E. van Duyse, A Dunjic, J. van der Merckt, A. Wambersie, and D. Werbrouck, 
Acquired Radioresistance, Radioselection, and Radioadaptation, Int. J. Rad. Biol., 
Suppi, Immediate Low Level Effects of Ionizing Radiations, Symposium Proceedings, 
Venice, June 22-26. 1959. pp. 183-194. Taylor & Francis Ltd., London. 1960. 

8. E. Krokowski and V. Taenzer, Der Radiogene Strahlenschutz Effekt, Strahlentherapie, 
130: 139-145 (1966). 

9. V. Taenzer and E. Krokowski, Acquired Radioresistance Following Whole Body 
Irradiation, Acta Radiol, Tber., Phys., Biol, 7(2): 88-96 (1968). 

10. E. Krokowski. Extraregionale Strahlenwirkungen, Strahlentherapie, 135: 193—201 
(1968). 

11. R. Roy Davies, The Effect of Dose Fractionation on Mutation Induction, 
Strahlenwirkung und Milieu, 160-170, 1962. 



SUMMARY OF RESEARCH ON FALLOUT 

EFFECTS ON CROP PLANTS 

IN THE FEDERAL REPUBLIC OF GERMANY 



( 



HELLMUT GLUBRECHT 

Institut fur Biophysik der Technischen Universitat Hannover and Institut fur Strahlen- 

botanik der Gesellschaft fur Strahlen- und Umweltforschung mbH, Munchen, Germany 



ABSTRACT 

Two groups of experiments are discussed. The first was concerned with effects of 
stratospheric fallout with relatively low activities (10 -9 to 10~ 4 Ci/m 2 /day). Various species 
of plants were exposed to continuing artificial 8 9 Sr, 9 ° Sr, or ' 3 7 Y fallout in special growth 
chambers. Uptake of the radionuclides by aboveground parts of the plants and by roots 
could be controlled, and the distribution in various plant organs was checked. Damaging 
effects could be observed only at activities of at least 10~ 5 Ci/m 2 /day. At lower fallout 
activities, however, some parameters (dry mass, plant height, etc.) were significantly 
increased as compared with the control. In the second group of experiments, the effects of 
external gamma irradiation were investigated in field experiments with barley, wheat, rye, 
and potatoes. Irradiation was performed at various stages of development and, on some 
cereals, also during hibernation. Parallel experiments on chronic exposure of the same crop 
species were carried out in a small gamma field. The results were in good agreement with 
data obtained by investigators in other countries. The radiation sensitivities of about 20 of 
the most common varieties of barley and wheat grown in West Germany were compared. 
Maximal differences of dose values resulting in the same degree of damage were ±30%. 



The effects of radioactive fallout on crop plants can be considered under two 
different points of view: 

1. Radioactive contamination of the crop and transfer of radioactivity to 
man by the food chain. 

2. Damaging effects on crop yield by external gamma and beta radiation as 
well as by radionuclides incorporated into the plants. 

It is now well known that, in the event of a nuclear war, the first group of 
effects would not play an important role as compared with the second group, at 
least as an acute hazard. The situation was different in the test explosions; 
cultivated land was reached only by tropospheric and stratospheric fallout, 

343 






344 GLUBRECHT 

and long time intervals had to be considered. In this case the fission products 
were soluble in water to a considerable degree, and long-lived radionuclides 
like 90 Sr and 137 Cs played a role. 

In the acute situation after detonation of an atomic bomb, the fallout 
components would be insoluble, and incorporation into plants would be 
negligible. However, stratospheric fallout would occur after some time, and then 
the hazards for areas far from the place of detonation of the nuclear explosions 
would have to be considered. 

In this paper two sets of experiments concerned with these two different 
situations are described. Nearly all the data given here are from our laboratory. 

EFFECTS OF SIMULATED STRATOSPHERIC 
FALLOUT ON PLANTS 

Experiments of this type were performed in our laboratory first by 
Niemann, 1 later by Naghedi— Ahmadi, 2 and most recently by Elmdust and 
Nassery. Basic data were derived from the maximal beta activity of fallout 
measured in West Germany, A , which was 3.7 nCi/m 2 /day. The activity of 
fallout solutions was given in multiples of A . 

The plants were grown under controlled conditions in glass boxes, and the 
fallout solution was sprayed on them daily by an automatic device (Fig. 1). The 
plants investigated in these experiments were: 

1. Lolium multiflorum Lam., as model of a pasture grass. 

2. Arabidopsis thaliana (L.) Heynh., for research on more than one 
generation. 

3. Kalanchoe blosfeldiana, for long-time studies on vegetatively propagated 
plants. 

The Sr, 8 Sr, and l 1 1 were applied as SrCl 2 and Nal in carrier-free solutions. 
Controls were treated with stable strontium and iodine. 

In Germany in 1963 the maximal concentration values of 90 Sr which had 
been observed were within 13% of the recommendations of the International 
Commission on Radiological Protection. The first question to be answered by 
our experiments was: Will the activity in the plants be increased proportionally 
at fallout activities of 10 to 10 6 A ? The answer is clearly "no" because: 

1. The radionuclides are taken up mainly by aboveground parts of the plants. 
This leads to saturation after a rather short time (Figs. 2 and 3). For 1 31 1 
the saturation values are less than proportional to the fallout activity 
(Fig. 4). 

2. Only 10 to 20% of the activity will be incorporated by the plants. If 20% 
of the soil surface is covered by plants, the total uptake is of the order of 
2 to 4%. This percentage becomes lower for fallout activities greater than 
10 5 A . 



SUMMARY OF RESEARCH ON FALLOUT EFFECTS 



345 




Fig. 1 Experimental device for treatment of plants with artificial fallout. 



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9 °Sr fallout. 



346 



GLUBRECHT 




5 10 15 20 

DAYS UNDER FALLOUT CONDITIONS 

Fig. 3 8 9 Sr contamination in rosette leaves of Arabidopsis thaliana (L.) 
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10 4 A ; -□-, 10 2 A 



SUMMARY OF RESEARCH ON FALLOUT EFFECTS 



347 



Therefore the main hazard of stratospheric fallout would be the continuous 
contamination of the soil. But uptake of long-lived radionuclides like 90 Sr and 
1 37 Cs would be limited by the reduced availability of these ions after they are 
absorbed in the soil. 4 

The next question concerned damaging actions of the radioactivity incorpo- 
rated in the plants. Radiation effects were observed at very low activities, as 
shown in Fig. 5, with the example of the flowering date of Arabidopsis. But 
these effects had the character of "stimulation." Other end points were 
influenced in a similar way; e.g., dry weight was 135% of control values at 50 A 
of 90 Sr. A good example of stimulation effects can be seen in Fig. 6, which 
shows control and treated Kalanchoe. 



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Damaging effects were never observed at fallout activities lower than 1(T 
A , which corresponds to 370 /jCi/m 2 /day. After 1 year 135 mCi/m 2 would be 
accumulated in the upper layers of the soil. Since in actuality l 7 Cs would be a 
component of stratospheric fallout in roughly the same concentration as Sr, 
the annual dose at 1 m above the soil surface may amount to about 10 krads. 
Therefore, as far as damaging effects on crop plants are concerned, the external 
radiation cannot be neglected even in the case of stratospheric fallout. 



EFFECTS OF EXTERNAL GAMMA IRRADIATION 
ON CROP PLANTS 



In the situation discussed in the foregoing paragraph, external irradiation by 
fallout residues would be of the character of chronic irradiation. After a nuclear 
explosion the local fallout would act more like acute irradiation. The simulation 



348 GLUBRECHT 




Fig. 6 Kalanchoe blosfeldiana exposed to 9 ° Sr fallout. Right, control treated 
with inactive strontium (5 x 10" 7 g Sr /liter); left, fallout activity 5 A = 
1.85 x 10" 8 Ci 90 Sr/m 2 /day. 



of the t l ' decay of early fission products has been achieved by Sparrow and 
co-workers. 5 According to their results reasonable data can also be obtained by 
constant-rate irradiation for 16 hr. 

We started experiments with chronic and acute irradiation of cereals — 
wheat, barley, rye — to obtain data on crops cultivated under natural conditions 
in our climate and to investigate the influence of various stages of development 
on radiation sensitivity. The acute irradiation time was 8 hr for all doses. 

The chronic irradiation was performed in a small gamma field with a 
10-Ci 1 Cs source. For acute irradiation a portable 300-kV X-ray machine was 
used. Dose variation was achieved in both cases by varying the distances between 
radiation source and plants. The stages of irradiation were: 

1. Two-leaf stage. 

2. Four-leaf stage. 

3. Posttillering. 

4. Ear emergence. 

5. Anthesis. 

Three repetitions were provided for each experiment, and the same experi- 
ment was repeated the following year. The varying climatic conditions in dif- 
ferent years had surprisingly little influence. 

The variation of radiation sensitivity at different stages was as striking as that 
observed by other investigators in pot experiments. One example of dose-effect 
curves is given in Fig. 7. Maximal sensitivity was always reached in either stage 3 
or 4. 



SUMMARY OF RESEARCH ON FALLOUT EFFECTS 



349 




DOSE, R 

Fig. 7 Effect of acute X irradiation at various stages of growth on the seed 

yield of winter wheat , four-leaf stage; , posttillering; , ear 

emergence; , anthesis. Yield of controls is 100%. 



Average exposures reducing grain yield to 50% of control are shown in Table 
1 for chronic and acute irradiation of three species of cereals. Grain yield is 
related to unit area, i.e., to a constant number of seeds. The difference between 
summer and winter varieties was very surprising. Winter wheat and winter rye 
have extremely high sensitivity at ear emergence. The summer crops, however, 
are more sensitive at the posttillering stage, the total dose applied during chronic 
irradiation being at least three times higher than the acute dose. The winter 
varieties were exposed to chronic irradiation throughout the whole time from 
sowing to harvest. Therefore the factor of difference here is considerably higher. 

During the winter the cereals are apparently rather resistant to irradiation, 
but temperature seems to play a small role compared with the stage of 
development. In one experiment irradiation of winter wheat during the two-leaf 
stage had to be performed at — 3°C in late February; in the other year it was in 
early April at 15 C. The dose values for equal effects were only 10% lower in the 
latter case. 

Different varieties of one species may vary in radiation sensitivity. It would 
be valuable to have especially resistant varieties. Greenhouse experiments have 
been made with 16 varieties of summer wheat grown in Germany. Irradiation 
was performed in the one-leaf stage (8 cm) with four dose values. After 8 weeks, 
plant height, dry mass, and number of tillers were checked. There was no 
deviation of more than 30% from the average values of all 16 varieties. The best 
way to avoid losses in crop yields in the case of a nuclear war seems to be to 
grow less-sensitive species. 



350 



GLUBRECHT 



Table 1 

AVERAGE EXPOSURE VALUES FOR 50% REDUCTION OF GRAIN YIELD OF 

VARIOUS CEREALS RECEIVING ACUTE IRRADIATION AT DIFFERENT STAGES OF 

DEVELOPMENT OR CHRONIC IRRADIATION 

Acute irradiation, R 



Chronic 
Two-leaf Four-leaf Ear irradiation 

Crop species stage stage Posttillering emergence Anthesis (total dose), R 



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5000 


3000 


1000 


1500 


3000 


3000 


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400 


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3500 


400 


300 


1500 


2400 



140 



120 — 







DOSE, R 

Fig. 8 Effect of chronic gamma irradiation at various stages of growth on the 

yield of potatoes germination (May 22— June 12); - - -. start of anthesis 

(June 12— July 1); , end of anthesis (July 1—20); , yellow stage 

(July 20-Aug. 9); , ripening (Aug. 9-29). 






( 



SUMMARY OF RESEARCH ON FALLOUT EFFECTS 351 

In this regard some results of Keppel 6 with potatoes should be mentioned. 
He simulated fallout radiation by spreading Co beads on the soil between the 
plants. The vegetative period was divided into five periods of about 3 weeks 
each, during which chronic irradiation was applied. Only the germination stage 
seemed to be sensitive in the dose range below 10,000 rads (Fig. 8). 

Much more data are needed for a complete evaluation of the problems of 
damage in crop plants in the case of a nuclear war, but basic research on the 
mechanisms of different radiosensitivities should not be neglected. 



REFERENCES 

1. E. 

370-375 (1961); also 8: 51-60 (1962). 

2. J. Naghedi-Ahmadi, Uber die Wirkung aus dem Fallout inkorporierter Radionuklide in 
Pflanzen, Thesis, Technischen Universitat Hannover, Germany, 1967. 

3. M. Elmdust and T. Nassery, Technischen Universitat Hannover, unpublished data. 

4. R. Scott Russell, Dietary Contamination, Its Significance in an Emergency, in 
Radiological Protection of the Public in a Nuclear Mass Disaster, H. Brunner and S. Pretre 
(Eds.), Proceedings of a Symposium, Interlaken, Switzerland, May 26-June 1, 1968, 
Report CONF-680507, pp. 279-306, Fachverband fuer Strahlenschutze e.V., 1968. 

5. A. H. Sparrow, Brenda Floyd, and P. J. Bottino, Effects of Simulated Radioactive Fallout 
Buildup and Decay on Survival and Yield of Lettuce, Maize, Radish, Squash, and Tomato, 
Radiat. Bot., 10: 445-455 (1970). 

6. H. Keppel, in Forschung im Geschaftsbereich des BML, Annual Report, Part Q, pp. 
125-126, Bonn, 1969. 



RADIATION DOSES TO VEGETATION 
FROM CLOSE-IN FALLOUT 
AT PROJECT SCHOONER 



W. A. RHOADS,* H. L. RAGSDALE,t R. B. PLATT,t and E. M. ROMNEYt 
*EG&G, Inc., Santa Barbara Division, Goleta, California; 
tEmory University, Atlanta, Georgia; and t University of California, 
Laboratory of Nuclear Medicine and Radiation Biology, Los Angeles, California 



ABSTRACT 

Project Schooner was a nuclear cratering experiment in the Plowshare Program for peaceful 
application of nuclear explosives. On the basis of information from two earlier experiments, 
Palanquin and Cabriolet, special dosimeters for measuring both beta and gamma radiation 
were placed in the open environment and on shrubs in the downwind area where fallout was 
anticipated. In addition, polyethylene sheets were placed over some shrubs to determine 
whether the shrubs could thus be protected against radiation damage. The gamma radiation 
doses for shrubs not covered were found to be essentially the same as the doses measured in 
the open and away from shrubs, but there was a 15% reduction in dose under the sheets. 
The beta doses to unsheltered vegetation were, however, reduced by almost 50% compared 
with doses at 25 cm in the open. This reduction was attributed to self-shielding. Beta doses 
to the shrubs were reduced still further, to 31% of the 25-cm beta dose in the open, by 
shielding the shrubs from direct fallout contamination. The estimated LD 5 q for Artemisia 
was 4449 rads, but the reduction in dose by the shelters was nearly sufficient to prevent 
damage to the shrubs, even though all other Artemisia shrubs in the center of the fallout 
pattern were killed. It was concluded that beta doses must be considered in protecting 
growing food crops and livestock and that even minimal shelter to prevent direct surface 
contamination would be of great importance. 



Project Schooner was a nuclear experiment in a layered tuffaceous medium, 
executed as a part of the Plowshare program for development of nuclear 
excavation. Detonation occurred Dec. 8, 1968, at 0800 (PST) in Area 20 of the 
Nevada Test Site (NTS). The resultant yield was 31 ± 4 kt (Ref. 1). Other details 
are published elsewhere. This paper is concerned only with radiation doses and 
their effects on vegetation along an arc of dosimetry stations approximately 
1800 m from ground zero (GZ). 

352 



RADIATION DOSES TO VEGETATION 353 

The vegetation in the area is dominated by Artemisia arbuscula and 
Artemisia tridentata, two species of the sagebrush which hybridize. A. tridentata 
was of primary interest at Schooner. Unfortunately, the junipers, which were of 
interest in the earlier studies at Palanquin and Cabriolet, 2 3 did not occur in the 
immediate downwind region of Schooner. Several other shrubs did occur, but 
only sporadically, and therefore were of little importance to this study. Artemisia 
has been previously shown to be a relatively sensitive shrub having an LD 100 
around 5500 rads (Ref. 3). Its occurrence in widespread and relatively pure 
stands makes it a good plant for use in the investigation of radiation effects. 

As background we will mention some results of two earlier experiments, 
Palanquin and Cabriolet, in the same geographical area. From Palanquin, 2 the 
first of these experiments, it was concluded that the vegetation damage was 
caused by radiation, probably mostly beta since the gamma-ray doses in much of 
the area, insofar as they could be derived, were too low to account for the 
extent of the damage. Another important result observed at Palanquin was the 
asymmetrical distribution of shrub damage, a damage pattern noted earlier in the 
Yucca Flat area of NTS by Shields and Wells. 4 In the areas peripheral to those 
where all or most plants were killed, this pattern of damage was a common 
characteristic; i.e., the plants were extensively damaged across the sides of the 
shrub toward GZ in the direction from which the fallout material was carried by 
the wind. In extreme cases only small branches or twigs remained alive; in other 
cases protection from rocks or larger shrubs and small trees sheltered whole 
plants from damage. 

At Cabriolet, 3 the second experiment of interest preceding Schooner, an 
extensive dosimetry program was undertaken to measure both beta and 
gamma-ray doses to the environment and to the vegetation. The special 
dosimetry designed by Kantz and Humpherys 3 for this program provided what 
appears to be the first opportunity to make comprehensive measurements in a 
field environment. 

Dose measurements were made by placing dosimeters in the open away from 
vegetation, on the fronts, tops, sides, and backs of shrubs and phantom plants. 
Some of the dose data from this experiment were presented by Kantz earlier in 
this symposium. 

The vegetation at Cabriolet showed a pattern of damage like that observed at 
Palanquin — the fronts of the shrubs were often damaged seriously, and, near the 
middle of the pattern, the Artemisia were entirely killed. This coincided with the 
pattern of doses, more particularly beta doses, observed there. It was concluded 
from this experiment that there was sufficient support for the hypothesis that 
beta radiation was primarily the cause of damage to the vegetation. This does 
not mean that gamma-ray doses were not important, however, since the two 
doses are additive. 

Both the Palanquin and Cabriolet devices were very small, less than 5 kt. The 
dosimetry stations were placed relatively close to GZ (at Cabriolet, about 610 m 
away) to ensure that the doses would be sufficiently great to be of interest. At 



354 RHOADS, RAGSDALE, PLATT, AND ROMNEY 

that distance the killed Artemisia covered a segment of the arc less than 150 m 
long. 

At Schooner, where the yield was relatively much greater, there was an 
opportunity to look at a larger irradiated area located in different terrain. The 
vegetation was also different although Artemisia remained the dominant species. 
In addition, Schooner presented an opportunity to test the hypothesis that, if 
beta radiation were a primary cause of damage to vegetation, then sheltering the 
vegetation from fallout should provide important protection. 



METHODS 

Fallout Dosimetry Stations 

Dosimeters were located at 97 stations along an arc north and east of the 
proposed GZ at distances from 1700 to more than 2000 m. Figure 1 shows the 
locations of the stations with respect to GZ and the terrain features important to 
this study. Referring to the aerial photograph of the area shown in Fig. 2, we can 
relate the size of the crater to the doses to the environment and to the effects of 
those doses. The solid lines in Fig. 1 indicate the boundaries of the canyon in 
which the dosimetry stations were located. The bottom of the canyon was 30 to 
100 m below the level of the land toward GZ and somewhat lower still than part 
of the area beyond the canyon. A combination of geography and the anticipated 
distances to which the base surge from the detonation was expected to reach 
determined the location of the stations. Although at the beginning of this 
experiment this very remote area of NTS was virtually without roads, trails, or 
other conventional landmarks, it was possible to enter the area with four-wheel- 
drive vehicles. 

The distance covered by the arc of stations shown in Fig. 1 was about 
2.8 km, and the distance between stations was approximately 35 m. These 
stations were placed in position 3 weeks before Schooner. At the same time, 
dosimeters that had been given measured doses were placed in the field as a 
check on dosimeter fading. One set of these dosimeters was removed from the 
field on D day, and another was removed when the dosimeters were collected 
from the fallout pattern. These provided tests both for accumulation of doses 
attributable to possible radiation from unknown sources and for dose fading due 
to sunlight and temperatures in the desert environment. No loss or increase in 
doses was observed from these dosimeter checks. 

Vegetation Shelters and Dosimetry 

In addition to the dosimeters placed in vertical arrays, four dosimeters were 
placed on sheltered shrubs and four on shrubs in the open. In each case one 
dosimeter was placed on the front (toward GZ) and one on the back of the 
shrub. Attempts were made to place the dosimeters on symmetrical shrubs that 



RADIATION DOSES TO VEGETATION 



355 



| 1 

N E VADA 




Fig. 1 Schooner crater and the location of the dosimetry stations to the 
north and east of it. 



were not close to other shrubs. Generally, this was not possible among the 
sheltered shrubs, because of the limited numbers available. 

Polyethylene sheets 6 m square and 6 mils thick were spread over as many 
Artemisia shrubs as could be covered conveniently at alternate stations along the 
arc. Figure 3 shows a protective sheet in place and also provides a general view of 
the terrain and vegetation. 

Fallout from Schooner occurred to the north and northeast of GZ. The 
dosimeter stations were within the edge of the base surge at the north but were 



356 



RHOADS, RAGSDALE, PLATT, AND ROMNEY 




Fig. 2 Aerial photograph of the Schooner area. The point at which the trail in 

the upper part of the photograph dead-ends at the cliff is the approximate 
center of the primary local fallout pattern. Station 6N is in the bottom of the 
canyon below that point. 



RADIATION DOSES TO VEGETATION 



357 




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358 RHOADS, RAGSDALE, PLATT, AND ROMNEY 

less so to the east. Some areas received an estimated fallout of up to 300 g/m 2 . 
Others received relatively little. 

On Dec. 20, 1968, at D + 12 days, all dosimeters were removed from the 
field and the shrubs were uncovered. At this time no differences were observed 
between the shrubs that were covered and those left exposed, except that those 
exposed were very dusty. 

Some of the polyethylene sheets were torn by heavy winds, but this damage 
was not severe except directly east of Schooner GZ at the mouth of the canyon, 
where, fortunately, the doses were too low to be of interest. At this time patches 
of snow, which had fallen about D + 7 days, still remained, and sometimes ice 
and snow mixed with fallout had to be removed along with the polyethylene 
sheets. 

All dosimeters were returned to the laboratory for readout on D + 23 days. 
Reading of the dosimeters began on D + 29 days. 



RESULTS 



Gamma-Ray Doses and Data on Radiological Safety Monitoring 

Figure 4 shows the dose rates at each dosimeter station as read from 
conventional instruments for radiological safety monitoring as the dosimeters 
were removed from the field. Also shown for comparison are the gamma-ray 
doses measured by the dosimeters at 1 m. The purpose of the comparison is to 
illustrate that postevent safety monitoring may not provide an adequate basis for 
dose estimates. If field doses were calculated from the safety monitoring 
dose-rate data by multiplying by some systematic factor, there would be a 
considerable discrepancy between the estimated and the measured doses. That 
the curves are not parallel is probably attributable to continued deposition and 
redistribution after the initial deposit of early postdetonation material with its 
resultant high infinite dose. 

Radiation Doses 25 Cm Above the Soil Surface 

Radiation doses were measured 25 cm above the soil surface since this was 
judged to be a height at which doses appeared to have the greatest effect on the 
local vegetation. Dose measurements were also made at the soil surface, but 
these varied widely because surface irregularities caused the fallout material to 
accumulate nonuniformly. This was particularly apparent in the reading of the 
beta doses since they were derived much more from sources near the irradiated 
object than were gamma-ray doses. This is because gamma-ray doses accrue from 
relatively large areas, whereas beta doses are affected primarily by particles on 
and nearby the surface of the irradiated objects. 






RADIATION DOSES TO VEGETATION 



359 





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The gamma-ray doses at 25 cm were essentially the same as those for 1 m 
(Fig. 4). The beta doses measured 25 cm aboveground by dosimeters placed on 
vertical wires away from vegetation are shown in Fig. 5. 

Figure 6 shows the ratios of the beta to gamma-ray doses obtained from 
these measurements. Two characteristics of these data are of interest. First, there 
appears to have been a systematic fluctuation in the dose ratio. Such a 
fluctuation was also observed at Cabriolet. The recurrence of this fluctuation is 



360 



RHOADS, RAGSDALE, PLATT, AND ROMNEY 



9 x 10 3 



6 x 10 3 



3 x 10 3 



30 N 



20 N 



N 



10 20 

STATION No. 



30 



40 



50 



Fig. 5 The beta radiation doses (in rads) measured at 25 cm above the soil 
surface in the fallout pattern of Schooner. 



probably more than chance; but, to be more than speculation, its explanation 
must come from those who design and execute the experiments. Second, the 
dose ratios are large, ranging from 5 to more than 14. Moreover, these ratios are 
slightly larger than those noted at Cabriolet, which ranged from 4 to 12.5. This 
difference may be due to an overestimate of gamma-ray doses at Cabriolet, or it 
may be due to differences in the source of the radioactive debris, i.e., in the 
device itself; discussion of the device is, of course, beyond the scope of this 
work. 



Doses to the Vegetation 



Gamma-Ray Doses 

Table 1 shows the doses for the main part of the central peak of radiation 
across the fallout pattern. Although there are differences at some stations 
between the gamma-ray doses at 25 cm and those measured on the shrubs, the 



RADIATION DOSES TO VEGETATION 



361 



15 



< 10 



30 N 



20 N 



N 



10 

STATION No. 



20 



30 



40 



50 



Fig. 6 The ratios of beta- to gamma-radiation doses (both in rads) in the 
Schooner fallout pattern. 



mean difference is essentially zero. The difference between the gamma doses at 
25 cm and those measured on the shrubs protected by the plastic sheets is 15%, 
however. This reduction might be anticipated considering the possibility of a 
low-energy gamma-ray component of the early postdetonation radioactive 
debris. 



Beta Doses 

The beta-dose data shown in Table 1, unlike the gamma-ray-dose data, 
indicate a reduction in the beta doses to the vegetation compared with the doses 
measured at 25 cm and away from the vegetation. In addition, the protection of 
the plastic sheets reduced the beta doses to the shrubs still further. Both 
reductions were large compared with the gamma-ray-dose reduction and were of 
important biological significance, as is shown subsequently. 



362 



RHOADS, RAGSDALE, PLATT, AND ROMNEY 



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RADIATION DOSES TO VEGETATION 363 

The decrease to 52.6% in shrub doses is attributed to "self -shielding," which 
can be envisioned in terms of the masses of vegetation shadowing themselves. 
Shrubs that were protected from the direct fallout contamination showed even 
larger reductions in beta doses, however. For the stations shown in Table 1, the 
covered shrubs received only 31.2% of the beta dose at 25 cm in the open and 
away from shrubs. 

Effects on the Vegetation 

The vegetation along the arc of dosimetry stations was examined at biweekly 
intervals for a period of 6 weeks after the dosimeters were taken from the field; 
thereafter it was examined at less frequent intervals. No differences between 
irradiated and nonirradiated vegetation were detectable until late April when an 
absence of inflorescence development was first noted. As was previously 
observed at Cabriolet, the first evidence that Artemisia had been affected could 
be seen only by a careful comparison of the nonirradiated with the irradiated 
shrubs. 

Experience has shown that a conspicuous characteristic of Artemisia is the 
occurrence of primordial inflorescences at the beginning of the active growing 
season, even though Artemisia does not come to anthesis until September in the 
test area. The leaf-color changes that appeared in mid-May and other phenotypic 
characteristics that . foretold complete defoliation and apparent death by 
September were not evident beforehand. 

By the end of June (D + 7 months), all the damage characteristics previously 
noted at Cabriolet were also apparent at Schooner in the most heavily irradiated 
parts of the fallout pattern. There were also notable differences, which will be 
discussed later. 

Protected and Unprotected Shrubs 

During the months of July and August, two surveys were made of the 
vegetation along the arc of the dosimeter stations. These surveys revealed that all 
Artemisia shrubs at Stations 4N, 6N, and 7N were killed, with the exception of 
those shrubs which had been covered with the plastic sheets. There was no 
damage to covered shrubs except at Station 6N, where four of the six shrubs 
covered had no damage and two had a small amount of defoliation. At all 
stations, 8N to 4 inclusively, around the arc, half or more of the uncovered 
Artemisia shrubs were 50 to 100% defoliated. Lesser damage was observed over 
many other stations. 

A 9-month LD 50 was derived from the August survey. The survey included 
all Artemisia shrubs within a 5-m radius of each dosimeter-support post. Eleven 
stations from 12N eastward to Station 13 were surveyed; only those stations at 
which either all or none of the Artemisia had been killed were excluded. The 
shrubs were grouped into two categories: (1) yellow brown to dark gray and 



364 



RHOADS, RAGSDALE, PLATT, AND ROMNEY 



dead or (2) gray green and living. Plants on the end of the radii with more than 
half their diameter beyond the 5-m limit were omitted. Those with more than 
half their diameter within the radii were counted. These counts were then used 
to determine the LD 50 by probit analysis. Data were determined from all 
stations even though half the stations did not have shrub doses determined by 
dosimeters on the shrubs. As shown in Fig. 7, the LD 50 was 7760 rads. When 



90 



70 



50 



30 



10 



Lethality 






^ 






Y = 1.908 + 0.000398 (x) 






x 2 - 10.64, 14 d. f. 






P = 0.7 






LD 5Q = 7760 rads 




— 


S\ i 




I 



DOSE, 10 J rads 

Fig. 7 The LD 5 q for Artemisia as of August 1969, 8 to 9 months postevent. 
The dose, reduced for the self -shielding factor, is 4449 rads. 



the beta dose is corrected by the factor 0.526 from Table 1, the dose becomes 
4449 rads if, from Fig. 6, the beta-to-gamma ratio is assumed to be 10. It was 
not possible to derive an LD 50 with equal precision at Cabriolet, but an LD 10 o 
for Cabriolet is nearly identical to the LD 100 for Schooner when the value for 
Schooner from the 25-cm dose is reduced by the self-shielding factor. Both 
values are 5500 rads. 



RADIATION DOSES TO VEGETATION 365 

Comparison of Sublethal Damage with That at Cabriolet 

In the peripheral parts of the fallout patterns of both Palanquin and 
Cabriolet, defoliation occurred in a characteristic pattern; 2 ' 3 i.e., the sides of the 
shrubs toward GZ and the tops of the shrubs were injured, but the backs 
remained relatively undamaged. At Schooner, however, along the arc of 
dosimeter stations, this pattern occurred infrequently, and another kind of 
damage pattern was observed. The lower twigs and branches all the way around 
the shrub were likely to be defoliated. An example of this is shown in Fig. 8, a 
photograph taken at D + 9 months. The extent of the damage appeared to be 
correlated with the dose, and, in extreme cases at higher doses, only a few 
branches or even a single branch remained alive. There were other patterns of 
damage also, but this was the most frequently encountered. The developing 
inflorescences that are approaching flowering can be seen at the top of the 
shrub. Yet the entire bottom half of the shrub is without leaves. The photograph 
was made at Station 32, where the shrubs recorded a dose of 3150 rads of beta 
and 700 rads of gamma radiation. 

CONCLUSIONS AND DISCUSSION 

Dose Reduction by Self-Shielding and Terrain 

At Schooner no consistent differences were detectable between the 
gamma-ray doses received by the shrubs and those measured on the vertical-array 
dosimeters away from the shrubs. This was also the case at Cabriolet. 

The relatively large reduction in beta-radiation dose to the vegetation 
compared with the 25-cm dose appears, however, to be higher than that 
observed at Cabriolet. Although doses were measured on both fronts and backs 
of the shrubs at Schooner also, it was not possible to distinguish a difference 
between these doses. This was quite unlike the circumstances at Cabriolet, where 
the fronts of the shrubs received larger doses than the backs. These dose 
differences are summarized in Table 2. There are several speculative explanations 
for these differences which may contribute to the better understanding of 
damage from fallout. 

Cabriolet fallout occurred across the front and sides of a low hill without a 
significant increase in elevation between the crater and the hottest part of the 
fallout pattern. At Schooner the vegetation was in the bottom of a canyon 
where the Artemisia shrubs were generally larger than those at Cabriolet. They 
also appeared to occur in relatively larger clumps with possibly more open space 
between them. These characteristics are attributable to the differences in the 
phenology and pedology encountered on the shallow soils of the exposed hillside 
compared with conditions on the alluvial bottoms of the canyons. 

It seems evident that fallout deposition varied as a result of terrain 
differences. On the exposed hillsides, where there were moderate winds, 



366 



RHOADS, RAGSDALE, PLATT, AND ROMNEY 




'-4- 

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RADIATION DOSES TO VEGETATION 367 



Table 2 

PERCENT BETA DOSE REDUCTION 
FROM THE 25-cm DOSE 

Means of fronts, 

tops,* and backs Backs only 

Schoonert -47.4 -47.4 

Cabriolet^ -18.4 ±11.3 -32.7 ±13.1 

* Doses were not measured in the tops of 
shrubs at Schooner. 

tFrom the values in Table 1. 

JMeans and standard deviation for 
Stations 1 to 7. 



differences in front to back were expected and were measured. (Differential 
deposition of airborne volcanic dust was noted by Miller. ) At Schooner, where 
the wind direction was essentially at a right angle to the canyon, the wind-borne 
fallout apparently was not deposited differentially from front to back of shrubs, 
and, as a result, no dose differences were distinguishable. 

The Cabriolet shrubs, which were subjected to winds in an open, exposed 
location, appear to have stopped more fallout than was deposited nearby, when 
compared with the shrubs at Schooner, which were protected from winds by the 
canyon, and the amounts of fallout deposited around them in the bottom of the 
canyon. The increased reduction in the dose to the back of Cabriolet shrubs may 
thus be both a measure of self-shielding in the conventional sense and a 
sheltering effect from wind patterns about the shrubs analogous on a microscale 
to conditions in the canyon at Schooner. Another possibility, for which we do 
not have data, is that under some conditions windswept surfaces may intercept 
less fallout; this is probably a function of surface roughness. 

Dose Reduction by Polyethylene Cover Sheets 

The relatively large reduction in dose resulting from use of 6-mil poly- 
ethylene sheets was not entirely anticipated. The gamma-ray-dose reduction of 
15.5% and the reduction of nearly 70% in beta dose must certainly be significant 
in terms of the subject of this symposium. Beta burns have been noted as an 
outstanding characteristic of fallout-radiation effects for both domestic ani- 
mals ,8 and men. 9 

Survival of Food Crops and Livestock 

The conditions resulting from close-in fallout under which this study was 
made, like those for Cabriolet and Palanquin, appear to be as nearly like 
conditions of nuclear warfare as can be simulated. In these experiments there 



368 RHOADS, RAGSDALE, PLATT, AND ROMNEY 

were depositions of large amounts of particulate materials containing nuclear 
debris which arrived near time zero. In the last few years, fallout-decay dose 
rates have only been simulated in the laboratory, and it has been shown that 
certain crop plants are more sensitive than was previously predicted under these 
conditions. 1 Since these experiments utilized only gamma radiation, there may 
be other effects associated with beta radiation and the higher beta energies of 
radioactive debris from near time zero not yet simulated in the laboratory. 

A few simple conclusions can be drawn. First, the relatively large doses to 
crops in the field, or to exposed seeds, from beta radiation must be considered. 
Perhaps some practical, simple dosimetry for beta radiation is needed. The large 
variations in the ratios of beta- to gamma-radiation doses and the possible errors 
in calculating doses from late postevent dose rates make beta-dose estimates 
difficult. These difficulties may decrease with increasing distances from GZ, but 
this is a problem for meteorologists, and for the present whether or not this 
occurs appears to be unknown. 

From the importance of beta radiation as an agent of damage, it follows that 
prevention of direct contamination by fallout particles is vital. Even a shield 
with as little mass as that afforded by 6 mils of polyethylene sheeting may be of 
critical importance. 

For livestock or crops that cannot be sheltered against direct contamination, 
the lee sides of any large object may provide some protection. It has frequently 
been observed that the presence of large shrubs and small trees decreased the 
airborne fallout damage to smaller shrubs downwind. In this matter geographical 
features themselves also appear to provide limited protection. 

Finally, it is obvious that more information from direct fallout effects will 
be very useful. 



ACKNOWLEDGMENTS 

This work was done under Contract No. AT(29-1)-1183 between Environ- 
mental Sciences Branch, Division of Biology and Medicine, U. S. Atomic Energy 
Commission, and EG&G, Inc., Santa Barbara Division. Part of the work was also 
done under Contract No. AT(40-1)-2412 between the USAEC and Emory 
University. 



REFERENCES 

1. L. R. Anspaugh et al., Bio-Medical Division Preliminary Report for Project Schooner, 
USAEC Report UCRL-50718, University of California, Livermore, July 22, 1969. 

2. W. A. Rhoads, R. B. Piatt, and R. A. Harvey, Radiosensitivity of Certain Perennial Shrub 
Species Based on a Study of the Nuclear Excavation Experiment Palanquin, with Other 
Observations of Effects on the Vegetation, USAEC Report CEX-68.4, EG&G, Inc., May 
1969. 



RADIATION DOSES TO VEGETATION 369 

3. W. A. Rhoads, R. B. Piatt, R. A. Harvey, and E. M. Romney, Ecological and 
Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and 
Short-Term Effects on the Vegetation from Close-in Fallout, USAEC Report PNE-956, 
EG&G, Inc., June 25, 1969. (Beta dosimetry methods are provided by A. D. Kantz and 
K. C. Humpherys in an appendix.) 

4. Lora M. Shields and Philip V. Wells, Effects of Nuclear Testing on Desert Vegetation, 
Science, 135: 38-40(1962). 

5. A. D. Kantz, Measurement of Beta Dose to Vegetation from Close-in Fallout, this 
volume. 

6. Carl F. Miller, The Contamination Behavior of Fallout-Like Particles Ejected by Volcano 
Irazu, Report AD-634901, Stanford Research Institute, April 1966. 

7. D. G. Brown and others, Late Effects in Cattle Exposed to Radioactive Fallout, Amer. J. 
Vet. Res., 27: 1509-1514 (1966). 

8. M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to 
Fallout Radiation, USAEC Report TID-24459, UT-AEC Agricultural Research Labora- 
tory, Sept. 7, 1967. 

9. Samuel Glasstone (Ed.), The Effects of Nuclear Weapons, rev. ed., USAEC Report 
ACCESS-127, p. 601, Defense Atomic Support Agency, 1962. 

10. A. H. Sparrow and Leanne Puglielli, Effects of Simulated Radioactive Fallout Decay on 
Growth and Yield of Cabbage, Maize, Peas, and Radish, Radiat. Bot., 9: 77-92 (1969). 



SURVIVAL AND YIELD OF CROP PLANTS 
FOLLOWING BETA IRRADIATION 



ROBERT K. SCHULZ 

Department of Soils and Plant Nutrition, University of California, Berkeley, California 

ABSTRACT 

Field experiments were carried out to investigate the effect of beta radiation on the growth 
of wheat, lettuce, and corn. The beta-radiation exposure was accomplished by fusing 90 Y 
onto 88- to 175-ju silica sand, and applying the sand to the crops with a remote-control 
applicator. Treatment levels on the wheat and lettuce crops ranged up to 59.4 mCi of 90 Y 
per square foot. In the corn experiment the highest level was 71.3 mCi of 90 Y per square 
foot. Wheat grain production was severely reduced when 6.6 mCi/sq ft of 90 Y was applied. 
This corresponds to approximately 2700 rads at the surface of the plant near the apical 
merrstem. Lettuce yields were reduced significantly only at the highest treatment level, 59.4 
mCi/sq ft, which corresponds to 9 300 rads at the plant surface near the apical meristem. 
Some abnormalities could be seen on the lettuce at the 6.6 mCi/sq ft treatment level. Corn 
yield was not reduced and plant appearance was not changed in any of the treatments. The 
apical meristem of the corn plant was protected by about 1 cm of tissue, and it hence 
received very little ionizing radiation. 



In the event of nuclear war, standing crops would be exposed to ionizing 
radiation from fallout containing both beta and gamma radiation in generally 
similar amounts. The study reported here is an investigation of the possible 
effects from the beta component. 

Extensive literature exists on the effects of gamma radiation on plants in 
contrast to the very limited information available concerning the effects of beta 
exposure to plants. 

It is widely accepted that the relative biological effectiveness (RBE) of beta 
to gamma doses is essentially unity 1 in the moderate and high beta energies 
found in fallout resulting from a nuclear detonation. This means that, when 
given ergs of energy are transferred to a fixed amount of tissue, deleterious 
effects will be the same whether the ionizing radiation is beta or gamma. In spite 
of this consideration, few predictions can be made of beta damage from gamma 
data, because of geometrical effects. The gamma exposure tends to be uniform 

370 



SURVIVAL AND YIELD OF CROP PLANTS 371 

throughout all the smaller plants, whereas beta exposure varies enormously 
because of absorption by plant tissue. Since the maximum range of the most 
energetic beta particles found in fallout is only a few millimeters in tissue, the 
more sensitive areas of the plant may receive little exposure to beta radiation. 
On the other hand, because of the fact that the beta energy is transferred to the 
tissue over a short path, the beta component could be very important where the 
sensitive plant parts are not protected. Rhoads et al. 2 have shown that the beta 
component in fallout at the Nevada Test Site has been primarily responsible for 
the death of some desert vegetation. 

Based on these considerations, it was felt that the beta investigation should 
be carried out under field conditions with normal plant densities and as normal 
an agricultural management as possible. In this work the effects of beta radiation 
on wheat, lettuce, and corn were investigated. 

MATERIALS AND METHODS 

The Kearney Horticultural Field Station of the University of California was 
used for carrying out the field research. Yttrium-90 was selected as the 
beta-emitting isotope because of its availability, its suitable half-life of 64.2 hr, 
and its average energy of 0.92 MeV. 

Although the half-life of 64.2 hr is somewhat longer than that of early 
fallout, Y was felt to be the best choice among available single isotopes to 
represent a fallout situation. It was decided to apply 90 Y to the crops as 
simulated fallout, i.e., fixed on 88- to 175-jU silica sand. Before the field 
experimentation could be initiated, three problems had to be solved. (1) 
Extreme radiochemical purity of the 90 Y fallout simulant had to be assured. 
The 90 Y was to be chemically separated from a 90 Sr— 90 Y mixture, and, owing 
to radiation-safety requirements, the residual 90 Sr radioactivity could not 
exceed 10~ 5 of the 90 Y activity. (2) A method of applying the fallout simulant 
evenly had to be developed. Since a number of curies would be involved in each 
experiment, radiation-safety considerations again were important. (3) A beta- 
radiation-dosimetry system had to be developed for measuring the beta doses 
delivered to the plants. 

Radiochemical Purity of the 90 Y Fallout Simulant 

The 88- to 1 75-^u sand contaminated with various levels of 90 Y was prepared 
by W. B. Lane of the Stanford Research Institute (SRI) at the Camp Parks Hot 
Cell facility. Basically Lane's method 3 consists of separation of 90 Y from a 
90 Sr— 90 Y mixture by precipitation of Sr(N0 3 ) 2 in concentrated nitric acid. 
Carrier-free 90 Y remaining in solution is then fused on the silica sand at 925°C. 
For radiation-safety considerations two modifications were made in this 
procedure. (1) The sand was eluted in water to remove all fine particles less than 
88 ji and returned to SRI for use in simulant preparation. (2) After the 90 Y was 



372 



SCHULZ 



separated from the 90 Sr— 90 Y mixture by SRI, it was purified in our laboratory 
to remove remaining traces of Sr contamination. The method used was a 
modification of the Brookhaven Y generator. 4 Essentially this purification 
depended on complexing the cation yttrium to an anion, yttrium citrate. 
Strontium carrier was added to the solution, and the solution was then passed 
over an ammonium-saturated cation-exchange column. This method results in an 
overall radiochemical separation of 90 Sr from 90 Y of greater than 10 7 . The 
purified 90 Y was then returned to SRI for fixing on the sand. 

Fallout-Simulant Applicator 

An apparatus that would apply the fine, highly radioactive sand evenly to 
the crops with safety to the operator had to be constructed. This required 
glove-box loading of the machine and remote operation of the applicator. The 
sand was to be applied at the rate of 10 g/sq ft on 4- by 4-ft plots. 

The essential part of the applicator consists of a 6-in.-wide hopper of 
triangular cross section. A four-vaned, notched stirrer was mounted at the 
bottom, and the sand was discharged through No. 60 drill holes (Fig. 1). Sand 
delivery was started and stopped by a hopper valve operated by a rotary 




Fig. 1 Sand hopper. Sand is agitated by notched stirrer and falls through 
No. 60 drill holes at bottom of hopper. Delivery of sand is started and stopped 
by solenoid-operated valve on bottom of hopper. 



SURVIVAL AND YIELD OF CROP PLANTS 



373 



solenoid. The rate of sand dispensing as a function of time is given in Fig. 2. It 
was found that, when 500 g of sand was placed in the hopper, the first 340 g was 
delivered at a uniform rate; then delivery became nonuniform. The delivery rate 
decreased, then increased briefly, and finally decreased again; this was not an 
experimental anomaly but a real, duplicable result. 




CUMULATIVE TIME, min 

Fig. 2 Sand delivery from hopper as a function of time. Hopper contained 
500 g 88- to 175-ju silica sand at start of run. 



The hopper or dispersing head is mounted on an apparatus that moves the 
head across the plot while laying down a 6-in. swath of sand (Fig. 3). Before 
each end of the pass, the hopper valve closes while the head is reversing 
direction. The whole apparatus moves perpendicular to the line of head travel so 
that, when the head has completed one cycle (i.e., across the plot and back), it 
has moved perpendicularly 6 in. This results in the uniform sand pattern 
depicted in Fig. 4. At the start and finish, there is a 6-in. by 4-ft isosceles triangle 
of single sand coverage. The rest of the area receives double coverage by the 
dispensing head. Speeds were calculated to give 10 g/sq ft. Actual rate of sand 
dispensing was checked by placing 30 1-qt ice-cream cartons within the 4- bv 
4-ft area. The amount of sand collected in each carton is given in Table 1. 
Standard deviation of a single value of 30 measurements was 0.09 g with a mean 



374 



SCHULZ 




Fig. 3 Complete sand applicator. Hopper moves back and forth across the 
plot laying down a 6-in. swath of sand while the whole apparatus moves 
perpendicular to the line of head travel. 



of 0.99 g per carton. This gives a calculated deposition of 10.3 g of sand per 
square foot. 



Beta-Radiation Dosimetry 

Development of a beta-radiation dosimetry system designed for use 
in the field was carried out with the cooperation of EG&G, Inc., Goleta, 
Calif. Micro-beta-radiation thermoluminescent dosimeters (TLD) consisting 
of CaF 2 — Mn chips sealed in thin, black polyethylene film were de- 
veloped. The dosimeters consist of approximately 0.25-mm cubes weighing 
approximately 40 [i. Initially the procedure consisted in reading the exposed 
dosimeters with an EG&G reader; each dosimeter was standardized after each 
reading by exposure to a standard cobalt source and again read out. This 
procedure was standardized against a primary standard electron source. This was 
done in two ways at the EG&G laboratory. Dosimeters were exposed to an 
electron beam from a Febetron, and the dose was calculated from the known 
energy and distance from the source. The dose was also determined by 
calorimetry. Finally, the dose was determined by the EG&G cobalt standardiza- 
tion readout procedure and compared with other results. The experiments were 
designed by Asher Kantz of EG&G. 



SURVIVAL AND YIELD OF CROP PLANTS 



375 



— H 6 in. I-*— 



Fig. 4 Diagram of sand coverage. Sand is applied to plot with 6-in.-vvide 
traveling head so that at the start and finish there is a 6-in. by 4-ft isosceles 
triangle of single sand coverage. The rest of the area receives double coverage. 



Table 1 
SAND COLLECTED BY 1-qt ICE-CREAM CARTONS 



Carton 


Weight of 


Carton 


Weight of 


Carton 


Weight of 


No. 


sand, g 


No. 


sand, g 


No. 


sand, g 


1 


1.0235 


11 


0.8026 


21 


0.8536 


2 


0.9308 


12 


1.0395 


22 


0.9358 


3 


1.2168 


13 


0.9187 


23 


0.9818 


4 


1.1159 


14 


1.0170 


24 


0.9625 


5 


1.0164 


15 


0.8650 


25 


0.9805 


6 


0.8861 


16 


1.0118 


26 


1.0298 


7 


1.0787 


17 


1.1521 


27 


1.0645 


8 


1.0758 


18 


0.9020 


28 


1.0345 


9 


1.0037 


19 


0.9312 


29 


0.9180 


10 


1.0563 


20 


0.9547 


30 


1.0422 



Average weight per carton = 0.9933 ±0.0911 



376 SCHULZ 

Table 2 
COMPARISON OF ABSORBED DOSE IN MICRO TLD CHIPS 



Distance from Febetron 
exit window to target, cm 


Predicted 
dose, krads 


Thermocouple 
dose, krads 


TLD 

dose, krads 


8.0 
3.0 


36.8 
313 


35.0 
270 


36.0 
306 



The electron source used was a Febetron 706, which is a field-emission diode 
device. The electrodes are charged to 600 keV, and the electrons are delivered in 
a 5-nsec pulse. The penetration of the electron beam has been measured and has 
the same characteristics as a 5 50-keV monoenergetic electron beam. The ratio of 
the dose to energy fluence from the beam was also measured, and again it was 
found that the energy was slightly above 500 keV. 

For satisfactory absorption characteristics, we found it necessary to maintain 
the target in a vacuum. At a given separation of the face of the electron tube and 
the target, the reproducibility of the absorbed dose from shot to shot was ±12%. 
For a series of experiments, a CaF 2 — Mn chip was placed in a known position in 
the electron beam. A chromel— constantan thermocouple (0.002-in. wire) was 
attached to the chip with a minimum of pliabond cement. The temperature rise 
experienced by the CaF 2 was recorded and the absorbed energy calculated. The 
thermocouple was then detached, and the amount of thermoluminescence in the 
chip was measured in a standard EG&G TLD reader. The energy absorption by 
the TLD measurement was calibrated against the response in a 60 Co-source 
range. Agreement of the electron energy absorption with the 60 Co energy 
deposition verifies that the energy absorption from the two sources is equal. To 
compare these measurements against the energy absorption predicted by the 
placement at a given position, we took a series of 3 to 5 shots for each 
measurement. The summary of the results of two such measurements is given 
in Table 2. 

The conditions of the electron source used for this experiment make it 
mandatory to have a CaF 2 chip that is thin compared with 500-keV electrons. 
The range of such electrons in CaF 2 is approximately 0.22 g/cm" or 0.028 in. 
Chips with a thickness from 0.007 to 0.015 in. were used for the thermocouple 
measurements. 

When the chips were broken into small volumes, the reproducibility was 
poor. Sawing the chips into 0.25-mm cubes gave a reproducibility within ±3% 
for a given chip. 

To save on expense and time, we developed our own standardization and 
readout procedure. For this purpose we purchased an EG&G model TL-003A 
TLD reader and outfitted it for reading the micro dosimeter chips. A 4-ir 
exposure chamber constructed for standardization of each dosimeter using 90 Y 



SURVIVAL AND YIELD OF CROP PLANTS 



377 



of known concentration is illustrated in Fig. 5. Basically, it consists of two lucite 
cylinders, each having a 1-in. wall thickness and a 1-in. lucite bottom. The top of 
each cylinder is covered with a 0.00025-in. -thick (approximately 0.64 mg/cm 2 ) 
Mylar membrane. The dosimeters are placed on the membrane so that the 
distance to any wall exceeds the maximum range of the Y radiation in water. 
The other cylinder is then inverted and secured to form a 477 -geometry exposure 
chamber. Standardized 90 Y is then carefully introduced into both halves of the 



DOSIMETERS EXPOSED 
BETWEEN TWO MYLAR 
MEMBRANES 0.00025 IN. 

THICK 7 FILLING AND 

REMOVAL BORES 




FILLING AND 
REMOVAL BORES 



Fig. 5 The 4tt chamber for exposing TLD dosimeters to a known amount of 
beta radiation. 90 Y solution concentrations ranged from 0.5 to 500 MCi/ml. 



chamber to completely fill the apparatus; there must be no entrapped air. After 
the dosimeters have been exposed for a given time, the 90 Y solution is 
transferred back into the 90 Y storage bottle. Both halves of the chamber are 
rinsed with dilute HCl and water and then dried by flowing warm, dry air 
through the system. This is done to prevent dilution of the 90 Y solution as it is 
successively used in repeated filling of the chamber for various exposures of the 
dosimeters. The apparatus is illustrated in Fig. 6. Appropriate traps, air dryers, 
and filters prevent contamination of the atmosphere by the vacuum and air lines 
used in filling and drying the apparatus. 

The 90 Y solutions were supplied by the SRI Camp Parks Hot Cell facility. 
The concentrations were determined in our laboratory both by comparison with 
a 9 ° Sr— 9 ° Y standard source from which the 9 ° Sr radiation was absorbed out and 
by comparison with a standard 2 P source. The agreement was to within 5%. A 
1-ml sample of Y was taken from the storage bottle before and after each use 
of the 90 Y in the 477 chamber to monitor for any losses of 90 Y from the 
solution by deposition on surfaces. 

In the first experiment with the apparatus, dosimeters were exposed for 
various times and at various 90 Y solution concentrations. The dose 
was computed with the aid of the equation given in Quimby and Feitelberg, 5 



378 



SCHULZ 




IN. LEAD 
SHIELD 



1-IN. LUCITE FRONT 



Fig. 6 Apparatus for filling, rinsing, and drying 4rr exposure chamber. 



Line to atmosphere 
Line to atmosphere 
Line to manometer 
Line for removal of en- 
trapped air (bottom 
chamber 
Large line for drying air 

(bottom chamber) 
Large line for drying air 

(top chamber) 
Drying-air exhaust line 
leading to filters 



A 


Line to lower three-way 


K 




stopcock 


L 


B 


Y introduction lines 


M 


C 


Line to sampling pipette 


N 


D 


Vacuum line for filling 
90 Y supply bottle 




E 


Line to acid-wash bottle 


O 


F 


Funnel for introduction of 






acid and water 


P 


G 


Drain line 




H 


Vacuum line 


Q 


I 
J 


477 chamber vacuum line 
Samples vacuum 





where D = 73.8 cE^T (c is the concentration, E^ is the average beta energy, and 
T is the time). 

The results of this experiment are plotted in Fig. 7; the calculated dose is 
plotted against the dose reported by EG&G. The points shown are averages of 
data from 10 to 15 different dosimeters. The 45° line is shown for comparison. 
These results are somewhat erratic, but the agreement was generally encouraging. 

In the next experiment a large number of dosimeters were again dosed at 
varying rates in the 4/T chamber and subsequently read out on the TLD reader. 
The results are shown in Fig. 8, in which the calculated dose is plotted against 



SURVIVAL AND YIELD OF CROP PLANTS 



379 




EG&G READING, rads 

Fig. 7 Calculated dose in the 47T exposure chamber plotted against dose 
reported by EG&G. 



the instrument reading. Again, each point is the average of a number of 
dosimeters receiving the same dose. The results again are somewhat erratic, but 
the relation appears to be linear. In future work we plan to calibrate each 
dosimeter individually to eliminate the variability caused by dosimeter size. 

To test the effectiveness of the polyethylene packaging, we dosed 
approximately 50 dosimeters equally in the 477 chamber and divided them into 
two lots. One lot was then exposed to the weather for a period of about 
2 months, and the other lot was kept as a control. Both lots were then read in 
the EG&G reader. If we use Fig. 8 as a calibration curve, the control chips read 
at 4730 rads and the exposed chips read at 4480 rads. For the purposes of our 
subsequent field experiments, in which the chips are exposed to weather, this 
difference is not important. 

Absorption of Y radiation by polyethylene was studied by placing 
polyethylene sheets of varying thickness between the chips and the Mylar 



380 



SCHULZ 




EG&G METER READING, rads 

Fig, 8 Calculated dose in the 47r exposure chamber plotted against the 
reading of .the EG&G instrument. 

membranes. Again using Fig. 8 as a calibration curve, we found the dose in rads. 
In these experiments the chips were packaged in 1.5-mil, black polyethylene, 
except for one case in which bare chips were exposed. The thickest polyethylene 
absorber was 0.5 in. The observed dose divided by the calculated dose from the 
47T exposure chamber was then plotted against the absorber thickness, as shown 
in Fig. 9. Note that evidently there is a maximum in the curve. The point plotted 
on the ordinate is for bare chips, however, and it is not known whether the 
lower value is due to exposure to light or to a dose-depth effect. The value on 
the ordinate is, of course, 100% at 1.5 mils since this was also the packaging used 
in establishing the calibration curve. 

EXPERIMENTAL DATA 



Preliminary Experiment 

Before designing the field experiments, we carried out a preliminary 
experiment in a controlled-environment chamber. This experiment utilized a 
wide range of 90 Y concentrations to determine the general levels at which 
beta-radiation damage to wheat and lettuce plants occurs. The radioactive sand 
was applied to foliage of 6-week-old plants growing in pots by entraining the 



SURVIVAL AND YIELD OF CROP PLANTS 



381 



100 




J_L 



25 50 100 



80 120 

ABSORBER THICKNESS, mils 



160 



200 



J I 



250 
APPROXIMATE RANGE, mg/cm : 



480 



90^ 



Fig. 9 Absorption of Y beta radiation by polyethylene sheets of varying 
thickness. 



sand in an air stream, employing a modification of Shelby's device, and then 
dropping the sand down a tube onto the plant foliage and soil surface. The 
treatment levels were such that 90 Y was added to the pots at the rate of 1.5, 
5.3, 17.5, 87, and 205 mCi/sq ft. The wheat was quite sensitive; grain 
production had ceased at the 17.5 mCi/sq ft level. Variability was rather large in 
this preliminary experiment, but the results were felt to be adequate to serve as a 
guide for planning the field experiments. The lettuce was somewhat more 
tolerant to 90 Y exposure; the yield began to decrease at the 17.5 mCi/sq ft level. 
From this level to the highest level used, 205 mCi/sq ft, there was a gradual 
decrease in yield. Visual aberrations to plant growth occurred at a much lower 
level of beta exposure. At the lowest level of treatment, 1.5 mCi/sq ft, some 
visual changes were noted, and at 5.3 mCi/sq ft obvious anatomical aberrations 
were present. 

Since visual changes in growth of the lettuce occurred at much lower levels 
than yield reduction, it was felt that microscopic examination of the apical 
meristems and other plant parts might prove interesting. Figure 10 is a 
photomicrograph of a normal apical meristem at the apex of the fleshy crown 
stem. Figure 11 gives detail of this meristem. Note that a single layer of cells 
forms the tunica, which overlies a corpus several cells thick. In normal tissues 
such as this, these cells are not vacuolated. Figure 12 shows a shoot meristem of 
a plant treated with 90 Y sand at 17.5 mCi/sq ft. Here there is no visible effect, 



382 



SCHULZ 





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SURVIVAL AND YIELD OF CROP PLANTS 



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384 SCHULZ 

even though the whole plant evidenced marked gross anatomical aberrations and 
yield reductions were becoming evident. Figure 13 shows one of a set of twin 
apexes found on a plant treated with 90 Y sand at 87 mCi/sq ft. This 
photomicrograph shows two abnormal shoot apexes formed in the axials of 
young leaves. The terminal meristem is at the upper left-hand corner. Figure 14 
is a detail of Fig. 13 which shows the upper of the two shoot apexes formed in 
the leaf axials. Note that this secondary meristem is itself damaged by radiation. 
The cells of the tunica and corpus are vacuolated. Figure 15 shows the shoot 
apex of a plant treated with Y sand at 205 mCi/sq ft. Here all cells are 
vacuolated and no cell division is occurring. Figure 16 shows cross section of 
young normal leaf near midrib. Note the prevalence of nonvacuolated cells in the 
epidermis and mesophyll. The bundle sheath surrounding the vascular bundle 
extends to form the rib of the leaf. The vascular bundle consists of, from top to 
bottom, xylem, phloem, and lactiferous ducts and fibers. Figure 17 shows a 
young leaf treated with 90 Y sand at 205 mCi/sq ft. Here the midrib is swollen 
because of vacuolation and swelling of mesophyll. Distinction between the 
bundle sheath and mesophyll is lost. 

Field Experiments 

The results of the preliminary experiment were used in the design of the 
field experiments carried out at the University of California Kearney 
Horticultural Field Station located near Fresno. The soil at the Kearney Station 
is a Hanford sandy loam formed on recent alluvium. The exchange capacity is 
about 5 milliequivalents per 100 g and is Ca 2+ dominated. The salt content is 
very low, and the area is generally one of high agricultural productivity. 

The field plots are described in Fig. 18. Each plot is 8 by 20 ft. The entire 
area is surrounded by a radiation-safe wire fence with a 6-ft reed fence attached 
to the wire for wind control. In the first experiment lettuce (Cos) or wheat 
(Pitic 62) was planted in each 8-ft by 20-ft plot, but only a 4- by 4-ft area in 
the center of each plot was contaminated. The beta exposure was by means of 
90 Y fused on 88- to 175-/J quartz sand at 925°C. This material was prepared by 
W. B. Lane at SRI. 

The wheat and lettuce were planted on Mar. 27, 1969, and the 90 Y sand was 
applied on May 16, 1969. The lettuce was harvested on June 10, 1969, 75 days 
after planting. The wheat was harvested on July 10, 1969, giving a growing 



period of 105 days. On the day of Y application, the lettuce had an average 
width of 18.7 cm, an average height of 14.5 cm, and an average weight of 56.3 g. 
At this time the wheat had an average height of 3 3 cm, and the apical meristems 
were approximately 1 cm above ground level. 

The sand was applied at rates of 0.26, 0.78, 2.25, 6.64, 19.8, and 59.4 mCi 
of 90 Y per square foot by remote control with the applicator previously 
described. Before the sand was applied, 212 micro dosimeters were placed at 
various locations in the plots, and their positions were recorded. The plots are 
shown at time of treatment in Fig. 19. 



SURVIVAL AND YIELD OF CROP PLANTS 



385 







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386 



SCHULZ 




Fig. 16 Cross section of normal young leaf. Note non- 
vacuolated cells in epidermis and mesophyll. (Magnification, 
150 X.) 














Fig. 17 Young leaf treated with 90 Y at 205 mCi/sq ft. 
Midrib is swollen, and distinction between bundle sheath and 
mesophyll is lost. (Magnification, 150 X.) 



SURVIVAL AND YIELD OF CROP PLANTS 



387 



■69' - 0' 



11' - 6' 






24' - 6' 






HI 



H 



H 



lh 



24' - 6' 



EACH TREAT- 
ED 4- BY 4-FT 
PLOT WAS 
SURROUNDED 
BY IDENTICAL 
•PLANTING 





RADIATION-SAFE 
FENCE. THREE 
STRANDS BARBED 
WIRE ABOVE 6-FT 
WELDED-WIRE 
MESH 

6-FT REED FENCE 
ATTACHED TO WIRE 
MESH FOR WIND 
CONTROL 



PLOT 

NO. 


CROP 


90 Y 

mCi/sq ft 


1 
2 
3 
4 


WHEAT 
LETTUCE 
WHEAT 
LETTUCE 


0.0 
0.0 
0.0 
0.0 


5 
6 
7 
8 


WHEAT 
LETTUCE 
WHEAT 
LETTUCE 


0.26 
0.26 
0.79 
0.79 


9 
10 
11 
12 


WHEAT 
LETTUCE 

WHEAT 
LETTUCE 


2.25 
2.25 
6.64 
6.64 . 


13 
14 
15 
16 


WHEAT 
LETTUCE 
WHEAT 
LETTUCE 


19.8 
19.8 
59.4 
59.4 






Fig. 18 Arrangement of field plots for J Y beta-radiation experiment at 



<>(), 



»(). 



Kearney Horticultural Field Station near Fresno, California. The Y was 
fused on 88- to 175-m quartz sand at 92 5°C. 




Fig. 20 Accumulation of radioactive sand on corn leaves. Sensitive parts of 
corn plants are well protected from beta radiation, and no damage occurred at 
the highest level of treatment (71.3 mCi/sq ft). 



SURVIVAL AND YIELD OF CROP PLANTS 



389 



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390 



SCHULZ 



Table 5 
LETTUCE YIELD DATA 



9 o y 
treatment. 


Plot No. 




Yield 


mCi/sq ft 


Fresh weight, g 


Dry weight, % 


Control 


4 


305.3 


7.0 


0.26 


6 


296.3 


6.5 


0.78 


8 


301.7 


6.4 


2.25 


10 


250.0 


7.2 


6.64 


12 


272.4 


6.4 


19.8 


14 


258.1 


8.2 


59.4 


16 


148.6 


11.1 



Dosimeters were placed on the plants as close as possible to the apical 
meristems and at 6 and 12 in. above the soil surface. The doses accrued during 
the experiment are given in Table 3. The yield data are given in Tables 4 and 5. 

After the wheat and lettuce were harvested, a corn experiment was carried 
out in the same area. The corn crop was contaminated with the radioactive sand 
34 days after planting. % At this time the apical meristem was about 2 3 cm above 
ground, and the plants were about 61 cm high and had a stem-base diameter of 
2 cm. The rate of sand application was 10 g/sq ft, as in the previous experiment, 
and the specific activity was varied to give 6.74, 12.9, 34.6, and 71.3 mCi/sq ft. 
Although the sand is spread evenly on the area, it accumulates on the plants 
unevenly as shown in Fig. 20. No yield reduction (5% level) was observed even in 
the highest level of treatment. 

DISCUSSION 



It is seen from the wheat data that at 6.64 mCi/sq ft (corresponding to 2700 
rads at the surface of the plant near the shoot meristem) grain production is 
severely reduced. Reduction in aerial growth, however, occurred only at the 
highest treatment level. In plot 13, there was no obvious damage to the plants 
other than the reduction in the grain. At the highest level, in plot 15, chlorotic 
leaves and stem shortening were observed. Photographs of tillers and grain from 
plot 13 are shown in Figs. 21 to 24. 

The lettuce plants are much less sensitive to the 90 Y treatment. Yield was 
reduced significantly only at the highest level of treatment. In this case the 
plants were stunted in appearance, and brown necrotic areas developed on the 
leaf edges. The center of many of the plants had no new growth; where bolting 
occurred, the leaves were distorted. Figure 25 shows a damaged lettuce plant 
from the highest contamination level. In Fig. 26 a plant from the same plot has 
resumed growth and shows multiple growing points. 



SURVIVAL AND YIELD OF CROP PLANTS 



391 




Fig. 21 Wheat head from control plot. 




Fig. 22 Wheat head from plant exposed to 90 Y at 19.8 mCi/sq ft. Color is 
much darker brown than control. 



392 



SCHULZ 



*4g$r&i*&W 



Fig. 2 3 Wheat grain from control plot. 




9 0. 



Fig. 24 Wheat grain from plot treated with yu Y at 19.8 mCi/sq ft 



The relation between the amount of radioactivity applied (in microcuries per 
square foot) and the dose (in rads) to the meristem for each crop is interesting 
(Fig. 2 7). In each case there is a linear relation between the applied radioactivity 
and the dose. 

Dosimeters tied near the apical meristem of the corn plants recorded a 
surface dose of about 5000 rads at the highest level of treatment, but the apical 
meristem was obviously well shielded by the large sheath protecting it. The 
protection afforded the shoot meristem can readily be seen by examination of 
the data presented in Fig. 9. This result suggests that consideration of the stage 
of development of the corn plant may be particularly important in assessing 
beta-radiation effects. In addition, the leaves exposed to the beta radiation were 



SURVIVAL AND YIELD OF CROP PLANTS 



393 




Fig. 25 Lettuce plant from plot treated with 90 Y at 59.4 mCi/sq ft. Damage 
was generalized with no apparent recovery, no new growth in center of plant. 




Fig. 26 Lettuce plant from same plot as that in Fig. 25. Note that in this 
plant some recovery has taken place in the center of the plant. The new 
growth consists of multiple growing points as contrasted to the single growing 
point normally found in lettuce plants. 



394 



SCHULZ 



10 : 



10' 



io- : 



10" 



10 
10 



Lettuce 




10 
'Y APPLIED, mCi/sq ft 



10- 



10- 



Fig. 27 Relation between 90 Y applied to plots and dose measured at apical 
meristem of plants. Data for both wheat and lettuce are for an average of four 
plants each. 



quite resistant to damage; no visual aberrations were discernible. During the 
period when cell division is taking place to produce the leaf, the meristematic 
tissue is well protected by the older, nonsensitive leaves. 

No plants were killed in any of these experiments, even at the highest levels 
of treatments. This is in agreement with the data of Schulz and 
Baldar 7 on wheat and lettuce exposed to beta radiation by immersion in 90 Y 
solutions. The apparent resistance of the plants to death by beta-radiation 
exposure is probably due to the uneven plant exposure. Some plant parts are 
relatively protected, and the plant does not receive a whole-plant exposure such 
as it would with gamma radiation. From the data accumulated so far, the 
beta-exposure survival level for agricultural crops appears to be far above the 
level necessary to cause severe yield reduction; therefore yield rather than 
survival is the important criterion in assessing beta damage to food crops. 



SURVIVAL AND YIELD OF CROP PLANTS 395 

ACKNOWLEDGMENTS 

This study was supported by the U. S. Atomic Energy Commission and the 
Office of Civil Defense, Department of the Army. 



REFERENCES 

I.E. H. Quimby and S. Feitelberg, Radioactive Isotopes in Medicine and Biology, Vol. 1. 
Basic Physics and Instrumentation, p. 142, Lea & Febiger, Philadelphia, 1963. 

2. W. A. Rhoads, R. B. Piatt, R. A. Harvey, and E. M. Romney, Ecological and 
Environmental Effects from Local Fallout from Cabriolet. I. Radiation Doses and 
Short-Term Effects on the Vegetation from Close-in Fallout, USAEC Report PNE-956, 
EG&G, Inc., June 25, 1969. 

3. W. B. Lane, Fallout Simulant Development, SRI Project No. MU-7236, Stanford Research 
Institute, 1969. (OCD Work Unit 321 1C.) 

4. R. F. Doering, W. D. Tucker, and L. G. Stang, Jr., A Simple Device for Milking High 
Parity Yttrium-90 from Strontium-90,./. Nucl. Med., 4: 54-59 (1963). 

5. E. H. Quimby and S. Feitelberg, Radioactive Isotopes in Medicine and Biology, Vol. 1, 
Basic Physics and Instrumentation, pp. 1 12-11 3, Lea and Febiger, Philadelphia, 1963. 

6. W. E. Shelby, J. L. Mackin, and R. K. Fuller, Artificial Surface Dirts for Detergency 
Studies with Painted Surfaces, Ind. Eng. Chem., 46: 2572 (1954). 

7. R. K. Schulz and N. Baldar, Beta Radiation Effects on Plants, paper presented at the 
Symposium on Vulnerability of Food Crops, and Livestock Production to Fallout 
Radiation, Colorado State University, Fort Collins, Colo., June 1969. 



FIELD STUDIES OF FALLOUT RETENTION 
BY PLANTS 



JOHN P. WITHERSPOON 

Ecological Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 



ABSTRACT 

Several field studies on the retention by plants of local fallout particles (particles exceeding 
44 )U in diameter) are summarized. 

Although initial fractions of fallout intercepted varied as a function of plant-foliage 
characteristics and particle size, average initial retention values are similar for studies done 
with a wide variety of plants in different geographical regions. 

Rapid losses of particles from foliage and other plant parts due to weathering occurred 
generally during the first week following initial particle deposition. Losses from tree species 
during this period were several times greater than losses from crop plants. In a period of 1 to 
2 weeks following deposition all plants lost 90% or more of the fallout particles initially 
intercepted. 

After about 3 weeks the loss of particles was relatively constant and proceeded at a slow 
rate (average weathering half-life of 21.3 ± 3.9 days) regardless of subsequent rain and wind 
conditions. 



The formulation of realistic predictions of the biological effects of fallout on 
vegetation requires information on both the radiosensitivity of plants exposed to 
radiation in fallout geometries and the capacity of vegetation to intercept and 
retain fallout particles. Since about 64% of the total radiation dose from fallout 
is delivered during the first week after detonation of a nuclear device, initial 
interception, sites of deposition, and early losses of particles are critical events in 
estimating dose to contaminated plants. 

This paper reviews some field studies on contamination of plants by local 
fallout and discusses the significance of these studies in the evaluation of 
short-term biological hazards involved in using nuclear devices for peaceful or 
military purposes. 

Studies on retention of local fallout particles by plants have been made 
under both varying geographic and varying particle-source conditions. However, 

396 



FIELD STUDIES OF FALLOUT RETENTION 397 

in many of these studies, the early losses of fallout from plants due to 
weathering have not been determined. This is particularly true of local fallout 
particles exceeding 44 jJl in diameter. Deposits of particles exceeding 44 (JL usually 
contain an appreciable fraction of fallout radioactivity, and they can represent a 
major source of radiation dose to plant tissues, although they may be briefly 
retained. Small particles constitute the bulk of radioactive debris deposited as 
worldwide fallout, but they lose much of their radioactivity via physical decay 
before deposition and are of greater biological significance as a major source of 
entry of radioactivity into food chains. 

INITIAL RETENTION OF FALLOUT BY PLANTS 

The initial retention of fallout by a given plant species depends on a number 
of factors. Such plant characteristics as surface area (mainly foliage), density, 
and surface characteristics of leaves are important variables. Meteorological 
conditions during deposition, particularly wind velocity and relative humidity, 
also influence initial retention. Finally, the size and amount of falling particles 
influence the degree to which plants are contaminated. Several field studies have 
been conducted in which the initial contamination of plants has been 
determined and related to one or more of these factors. 

The initial retention of fallout by plants can be expressed in two ways. One 
is the foliage contamination factor (a/) used by Miller: 1 

a/ = Ci°/mi sqft/g (1 ) 

where Ci is the quantity in microcuries of radionuclide initially intercepted per 
gram of dry weight of foliage and rrij is the quantity in microcuries of 
radionuclide deposited per square foot of soil surface area. Another expression 
of initial retention is the fraction (F) of fallout which is intercepted by plants or 
foliage: 

F = a/w/ (2) 

where w/ is the biomass of foliage, or of the plant, in grams per square foot of 
soil surface area. 

Values of a/ for plants sampled after nuclear tests have been smaller than 
values reported in other field tests where nonnuclear sources of fallout were 
applied. Miller, 1 reviewing a/ values for plants sampled following weapons tests, 
reported a range of 2 X lCf 5 to 0.013 sq ft/g. Other estimates have been made 
by Martin. 2 Values from three weapons tests (Priscilla, Buffalo Round 2, and 
Sedan) ranged from 0.002 to 0.012, with an average of 0.004 sq ft/g. Most of 
the plant samples taken after nuclear detonations were collected several days 
after initial deposition of fallout or after some losses due to weathering had 



398 



WITHERSPOON 



occurred. Also, results from test-site fallout fields were usually obtained in areas 
of light to moderate fallout. 

Plant contamination values derived from several field studies with local 
fallout and, where samples were taken before appreciable weathering, are fairly 
consistent. The a/ values for a variety of different plant species were taken by 
Miller 1 in Costa Rica following deposition of fallout from the Irazu volcano. A 
median value of 0.05 sq ft/g was reported for dry exposure conditions and 
particles having a median diameter between 50 and 100 ju. In studies at Oak 
Ridge National Laboratory, Witherspoon and Taylor 3 reported an average a/ 
value of 0.05 7 ± 0.024 sq ft/g for five species of crop plants treated with 88- to 
175-fJ. diameter particles. In similar studies 4 values of 0.035 and 0.005 sq ft/g 
were reported for oak and pine tree foliage, respectively. Values for relatively 
small-leaved plants such as pine 4 (0.005), lespedeza 3 (0.010), and fescue grass 5 
(0.011) tend to be smaller than those for large-leaved plants. 

Therefore an a/ value of 0.05 sq ft/g seems reasonable for calculating initial 
beta-exposure doses to plants in areas of local, dry fallout deposition (or where 
particles exceed 50 /i in diameter). A value of about 0.01 may represent a good 
estimate for most narrow-leaved plants. Under damp conditions (relative 
humidity greater than 90%), or where foliage surfaces are wet, a/ values have 
been reported to increase by an average of two to four times those obtained 
under dry conditions. 1 ' 6 

Reported values of F, initial fraction of fallout intercepted by plants relative 
to amount deposited per open soil surface area, are summarized in Table 1. 



Table 1 

INITIAL RETENTION OF SIMULATED FALLOUT DEPOSITED IN AN ACUTE 
MODE UNDER DRY CONDITIONS 







Retention, % 




Foliage area 








44- to 88-u 


88- to 175-u 


175- to 350-u 


Soil surface area 


Plar 


t density, 


Plant 


particles 


particles 


particles 


sq ft/sq ft 


g/sc 


ft of soil 


White pine 4 * 




24.2 








44.6 


Red oak 




34.9 








9.9 


Squash 


100.0 


88.5 




1.72 




6.4 


Soybean 


100.0 


100.0 




3.11 




11.4 


Lespedeza 


7.5 


1.9 




0.51 




1.9 


Peanut 


9.8 


5.8 




0.91 




4.4 


Sorghum 


48.9 


10.8 




1.25 




5.4 


Fescue 


45.4 


19.6 








17.4 


Pasture grass 




7.4 


5.5 






9.2 


Alfalfa 6 




23.0 


5.0 






19.5 


Corn 




44.0 











* Reference number. 



FIELD STUDIES OF FALLOUT RETENTION 399 

Initial retention can be seen to vary both with plant-foliage types and with 
particle size. Where retention values for different particle sizes can be compared, 
there is an average of two to three times less initial retention when particle size 
range is increased by a factor of 2. This is particularly evident in plants having 
small leaves and small foliage surface area relative to soil surface area. Mass 
loading of particles used in the studies summarized in Table 1 varied from about 
0.5 to 13.6 g of particles per square foot of open soil surface. In one series of 
studies 6 where mass loading was varied, initial retention was found to be 
independent of mass loading over this range. 

Sites of retention other than foliage can be important in determining 
biological effects of fallout radiation on plant species. Table 2 gives the average 

Table 2 
FRACTION OF TOTAL INITIAL RETENTION IN PLANT PARTS* 

Fraction of Fraction of 

Plant Plant part 44- to 88-ju particles 88- to 175-ju particles 

0.037 
0.032 
0.931 

0.086 
0.914 

0.160 
0.840 

*Fallout applied under dry conditions at a mass loading of from 4.5 to 
6.6 g per square foot of open soil surface. 



fraction of total initial retention associated with various plant parts. For these 
particular species the foliage intercepted most of the fallout, but small fractions 
were intercepted by radiosensitive structures such as flowers and buds. In the 
white pine, a relatively radiosensitive plant species, a large fraction of fallout is 
trapped in clusters of buds on the ends of branches. Since these buds contain 
meristematic tissues, which are the most radiosensitive parts of the vegetating 
plant, these trapping sites represent critical regions. Particles trapped in these 
structures also are retained longer than particles intercepted by pine foliage. 4 
Flowers also may intercept small fractions of fallout. In squash plants, Table 2, 
initial interception by flowers of particles 44 to 88 jjl in diameter was less than 
that of 88- to 175-jU particles applied at the same mass loading. The larger 
particles may have had a tendency to bounce or roll off foliage into open 
flowers, whereas smaller particles were more efficiently intercepted by foliage 
and stem surfaces. Smaller particles, in the 44- to 88-yU range, were intercepted 
by vertical structures, such as sorghum stalks, with much greater efficiency than 



Squash 


Stem 


0.051 




Flowers 


0.007 




Foliage 


0.942 


Sorghum 


Stalk 


0.259 




Foliage 


0.741 


White pine 


Bud clusters 
Foliage 





400 



WITHERSPOON 



larger particles. Grasslike plants such as sorghum, corn, and fescue have effective 
particle-trapping sites in the leaf axils, angles between the leaves and stems. 3 ' 5 ' 6 
Unless particles contain enough radioactivity to produce damage to tissue from 
contact doses, however, these trapping sites may not be biologically important 
since they are somewhat removed from more radiosensitive meristematic regions. 

LOSS OF FALLOUT FROM PLANTS DUE TO WEATHERING 

The major meteorological factors that influence retention of fallout by 
plants are wind speed and rainfall. Estimation of early losses of fallout particles 
from plants, particularly for the first week following initial deposition, is critical 
in determining dose to contaminated plants. Results from studies on retention 
indicate that concentrations of radionuclides on fallout-contaminated plants can 
be expected. to decrease at rates significantly higher than would be predicted on 
the basis of physical, radioactive decay. Beta-radiation-exposure geometries may 
be expected to change rapidly from a contact to a bath mode of exposure. 

Loss of fallout from foliage during the first day following deposition is rapid 
under dry conditions with relatively gentle wind speeds. Table 3 illustrates 

Table 3 
PROMPT LOSSES OF 88- TO 175-u PARTICLES FROM FOLIAGE 





Time after 


Initial 


interception 


Wind, 


Rain, 


Plant 


deposition, hr 


remaining, 


% 


mph 


in. 


Com 6 * 




24 




94 




to 20 




Alfalfa 6 




24 




82 




to 20 




Squash 




36 




52 




to 5 




Soybean 




36 




49 




to 5 




Sorghum 




36 




90 




to 5 




Peanut 




36 




44 




to 5 




Lespedeza 




36 




74 




to 5 




Fescue 




18 




34 




to 1.5 




White pine 




1 




90 




to 12 




White pine 




24 




6.3 




to 15 


0.9 


Red oak 4 




1 




9.5 




to 12 




Red oak 




24 




0.4 




Oto 15 


0.9 



Reference number. 



prompt losses for 10 plant species studied under similar conditions of deposition 
mode and weather. In most cases these losses amount to 50% or more of the 
amounts initially intercepted. Studies with smaller particles (44 to 88 fJ.) have 
indicated that first-day losses are as great as with 88- to 175-jLt particles. 3 Rapid 
particle loss from other plant structures also may be expected. Table 4 gives 



FIELD STUDIES OF FALLOUT RETENTION 



401 



Table 4 

LOSSES OF 88- TO 175-ju PARTICLES FROM SQUASH AND 
SORGHUM DUE TO WIND ACTION 





Wind, 
mph 




Retention, %* 




Time, 




Squash 




Sorghum 


days 


Foliage 


Flowers 


Stem 


Foliage Stalk 


0.5 

1.5 

7 


to 5 
to 5 
to 7 


86.2 
52.4 
36.0 


37.5 
14.8 
10.0 


93.0 
90.0 

44.1 


96.8 53.4 
90.0 33.8 
47.0 2.6 



Percent of initial interception value. 



retention values for stem and flowers of squash and for sorghum stalks. Rate of 
loss of particles from squash foliage was greater than that from the stem over a 
period of 1 week after initial deposition. It is probable that stems, which are 
prostrate and under the large leaves, intercepted some of the particles dislodged 
from foliage by gentle winds during this period. The more rapid loss rate from 
flowers was due, in this case, to wilting and loss of petals during this period — a 
phenological event. Rapid losses from structures such as the vertical stalks of 
sorghum were expected. 

Some generalizations concerning the probable retention of fallout by trees 
vs. agricultural plants may be made. Table 5 gives average foliage-retention values 
for five crop species 3 that vary in growth habit and leaf-surface characteristics 
and for two tree species that represent very common tree-foliage types. Initial 



Table 5 

AVERAGE RETENTION* OF 88- TO 175-ju PARTICLES BY PLANTS UP TO 
5 WEEKS AFTER DEPOSITION 





Average 










Time after 

application, 

days 


retention of 

five crop 

species, % 


Accumulated 

rainfall, 

in. 


Average 


retention, % 


Accumulated 
rainfall, 


4 

White pine 


Red oak 


in. 


0.04 







91.0 ± 10.0 


9.50 ±0.81 





1 


74.0 ± 8.3 





6.3 ±0.8 


0.39 ±0.06 


0.90 


1.5 


61.8 ±8.7 





4.5 ±0.4 


0.25 ±0.04 


0.90 


7 


33.0±4.6 


0.25 


2.5 ±0.2 


0.02 ±0.003 


1.30 


14 


9.4 ±4.7 


1.28 


2.1 ±0.2 


0.015 ±0.001 


1.43 


21 


2.7 ± 1.2 


2.67 


1.9 ±0.3 


0.012 ±0.001 


1.47 


28 


2.6 ± 1.5 


2.67 


1.6 ±0.2 


0.010 ±0.002 


2.88 


35 


2.6 ± 1.6 


2.67 


1.2 ±0.1 


0.010 ±0.002 


3.46 



* Average percent of initial interception ± 1 standard error. 



402 WITHERSPOON 

particle losses, up to 1 week, were much greater for the trees. The data for trees 
reflect, however, the effects of one rain which fell 12 hr after initial deposition. 
The losses from crop plants for the first 6 days were due to wind action only. 
Nevertheless, with comparable rainfall for the duration of these studies, up to 
5 weeks after deposition, losses from trees were greater. Smooth-leaved trees, 
such as the red oak, retained only a small fraction of the initial deposition after 
1 week. All these plants lost the major portion (90%) of the fallout in 1 to 2 
weeks, a period in which the major portion of fallout-radiation dose is delivered. 
Not only did the trees lose particles faster than the crop species tested but also, 
from the standpoint of dose, this loss is more important for trees. Particle loss 
can also be interpreted as a change in beta-exposure geometry from a contact to 
a bath mode, and the most radiosensitive structures (meristems and flowers) are 
located at greater distances from the ground in trees than in crop plants. 
Therefore bath doses from fallout on the ground would be less serious, impart 
less dose, to trees than to crop plants because of their relatively greater height. 

Retention of particles beyond 2 weeks was relatively stable for trees and 
crop plants regardless of amount of wind and rainfall. By this time most of the 
fallout has probably become trapped in sites upon which subsequent weathering 
has little effect. Retention characteristics after this time may be important from 
the standpoint of chronic low-level dose or transfer into food chains. 

Data on fallout retention of plants or plant parts plotted vs. time typically 
take the form of an exponential curve. In the calculation of half-lives, however, 
it is difficult to express these data in terms of a singie weathering or effective 
half-life. 4 Rapid particle losses during the first day or week and suDsequent 
loss-rate changes after early weathering imply that retention data should be 
compartmentalized into appropriate time components for half-life analyses. 
Table 6 gives weathering half-lives for 88- to 175-/i particles on seven species of 
plants. These half-lives are given for three time components: initial deposition to 
1.5 days, when very rapid loss rates occur; 1.5 to 14 days; and 14 to 33 days, 
when loss rates tend to stabilize at a very slow rate. Averaging these weathering 
half-lives gives some indication of general particle retention for a wide variety of 
plants. Such averages may be useful in dose calculations for periods up to several 
weeks following deposition. 

Environmental half-lives (e.g., half-life rates of loss due to causes other than 
radioactive decay) of radionuclides on fallout-contaminated plants were reported 
by Martin 7 for plants in the Sedan fallout field. Bartlett et al. 8 reported these 
values for plants sprayed with fission-product solutions. In the Sedan fallout 
field from 5 to 30 days after detonation, the environmental half-lives for fallout 
39 Sr and 131 I were 28 and 13 to 17 days, respectively. 7 Fission products 
sprayed on grass exposed to wind and rain up to 60 days had an average 
environmental half-life of about 14 days. 8 

The average weathering half-life for the 14- to 3 3 -day time component in 
Table 6 is 21.3 ± 3.9 days. Thus it appears that weathering or environmental 
half-life values for different kinds of vegetation growing in different geographical 



FIELD STUDIES OF FALLOUT RETENTION 



403 



Table 6 

WEATHERING HALF-LIVES OF 88- TO 175-jU PARTICLES ON FOLIAGE 
FOR THREE TIME COMPONENTS 





Half-life 




Half -life 




Half-life 






for to 




for 1.5 to 




for 14 to 






1.5 days, 


Rain, 


14 days, 


Rain, 


33 days, 


Rain, 


Plant 


days, 


in. 


days, 


in. 


days, 


in. 


White pine 4 * 


0.69 


0.9 


13.09 


1.43 


26.14 


1.97 


Red oak 


0.64 


0.9 


6.11 


1.43 


42.58 


1.97 


Squash 


1.62 





7.36 


1.28 


15.06 


1.39 


Soybean 


1.47 





7.19 


1.28 


15.97 


1.39 


Sorghum 


4.10 





7.43 


1.28 


19.43 


1.39 


Peanut 


1.33 





15.71 


1.28 


16.07 


1.39 


Lespedeza 


2.88 





7.55 


1.28 


14.07 


1.39 


Average ±1 














standard error 


1.82 ±0.48 




9.20 ± 1.33 




21.33 ± 3.96 





Reference number. 



regions may be similar- after the rapid initial losses during the first week or so 
have occurred. The average values for different species (1.82 ± 0.48 days for the 
0- to 1.5-day component and 9.20 ±1.33 days for the 1.5- to 14-day 
component) and the ranges given in Table 6 suggest that weathering half-lives 
may differ only by a factor of slightly over 1 to about 6.5 between species 
during the periods of rapid initial particle loss. 

The similarities in results from field studies in which particle size 
approximates that of local fallout are striking. Both initial contamination 
factors, such as the a/ value, and weathering half-lives for time components may 
be in close enough agreement so that the use of averages, such as those presented 
here, would give reasonable estimates of dose from fallout when used in 
appropriate models. 

ACKNOWLEDGMENT 

This research was sponsored by the U. S. Atomic Energy Commission under 
contract with Union Carbide Corporation and the Office of Civil Defense, 
Department of Defense. 



REFERENCES 



1. C. F. Miller and H. Lee, Operation Ceniza-Arena. Part One, SRI Project MU-4890, 
Stanford Research Institute, 1966. 



404 WITHERSPOON 

2. W. E. Martin, Early Food-Chain Kinetics of Radionuclides Following Close-In Fallout 
from a Single Nuclear Detonation, in Radioactive Fallout from Nuclear Weapons Tests, 
Germantown, Md., Nov. 3-6, 1964, A. W. Klement (Editor), AEC Symposium Series, 
No. 5 (CONF-765), 1965. 

3. J. P. Witherspoon and F. G. Taylor, Interception and Retention of a Simulated Fallout by 
Agricultural Plants, Health Pbys., 19: 493-499 (1970). 

13 7 

4. J. P. Witherspoon and F. G. Taylor, Retention of a Fallout Simulant Containing Cs by 
Pine and Oak Trees, Health Phys., 17: 825-829 (1969). 

5. R. C. Dahlman, in Progress Report in Postattack Ecology. Interim Report, USAEC 
Report ORNL-TM-2983, Oak Ridge National Laboratory, December 1970. 

6. J. E. Johnson and A. I. Lovaas, Deposition and Retention of Simulated Near-In Fallout 
by Food Crops and Livestock, Technical Progress Report 3 223C, Colorado State 
University, 1969. 

7. W. E. Martin, Losses of Sr, Sr and I from Fallout-Contaminated Plants, Health 
Phys., 4: 275-284 (1964). 

8. B. O. Bartlett, L. F. Middleton, G. M. Milbourn, and H. M. Squire, The Removal of 
Fission Products from Grass by Rain, in Surveys of Radioactivity in Human Diet and 
Experimental Studies, British Report ARCRL-5, pp. 52-54, 1961. 



RETENTION OF NEAR-IN FALLOUT 
BY CROPS 



A. I. LOVAAS and J. E. JOHNSON 

Colorado State University, Fort Collins, Colorado 



ABSTRACT 

Near-in fallout simulant, 88- to 175- and 175- to 350-^ sand labeled with ,77 Lu, was 
dispersed over field crops. Initial retention and weathering half-time were measured for 
alfalfa, corn, barley, bromegrass, sudan grass, and sugar-beet tops. 



Papers in this session have considered the biological effects of gamma and beta 
radiation on plants, especially crop plants, with the intent of evaluating 
parameters for models that postulate biological consequences of fallout 
radiation. 1 Constantin, Siemer, and Killion* showed the stage specific effects on 
uniformly administered gamma radiation. Bottino and Sparrow* extended the 
study of biological effects to a gamma field decreasing in intensity over time. 
Rhoads et al.* described combined gamma and beta effects of actual test-site 
fallout. Both Shulz* and Witherspoon* dealt with the biological effects of 
applied deposits of beta-emitting fallout simulant. This report is on retention 
experiments employing a material similar to that used by Witherspoon. Our 
interest is in bulk contamination of potential animal feed as well as in the finer 
features of particle retention on plants. 2 A body of related data on volcano dust 
has been detailed by Miller's group 3 at Sanford Research Institute (SRI). 

BACKGROUND 

We have studied the capacity of plant canopies to retain sand-size falloutlike 
particles. A simulant was chosen to be similar to material swept into the air by a 
nuclear blast over a silicate-soil region. Of all the particles produced by or swept 



This volume. 

405 



406 LOVAAS AND JOHNSON 

into a nuclear cloud, we are concerned with those in the size range of 100 jLl, i.e., 
near-in or local fallout as distinguished from the worldwide variety. 4 Particles 
much smaller than 20 to 40 /i are preferentially carried beyond near-in deposits, 
whereas particles of several hundred microns, i.e., approaching 1 mm, are rapidly 
depleted. 5 We used batches of sand of 88 to 175 and 175 to 350^ for these 
exposures. The sand is from the reserve of fallout-simulant materials maintained 
and supplied by SRI. 

Two processes may be considered to constitute the mechanism of external 
retention of particles by plants. Small particles adhere to rough or sticky 
surfaces, and cupping structures are effective means of holding the larger 
particles that would otherwise bounce or roll off. Both the initial retention 
governed by these two processes and the lasting retentive properties of plant 
surfaces and structures are modified by weathering, observably by the wetting of 
rain, buffeting by wind, and tearing by hail. 

OBJECTIVES AND EXPERIMENTS 

At Colorado State University our field experiments seek to show initial and 
persistent retention characteristics of species, some weather effects on initial 
retention, and the step changes they cause in retention functions. We exposed 
standing field crops to the simulant of near-in fallout. Radioactivity was used 
only as a particle tracer and not to produce biological effect. 

The study attempted to simulate portions of near-in fallout derived from 
silicate soil in respect to particulate material, particle size, particle fall 
conditions, and amount of deposited material (mass load). Since we wished to 
follow foliar deposits of particles and not foliar absorption of radionuclides, an 
essentially insoluble form of radiotracer was used. The nuclide employed was 
1 77 Lu. This labeled material was prepared by W. B. Lane of SRI. 6 

In the winter of the first crop year of our study, some nonradioactive 
releases were carried out in an enclosed chamber (Fig. 1). This permitted the 
determination of retention under conditions of still air and controlled surface 
moisture (Fig. 2). Plants for the chamber releases were from greenhouse stock. 
Chamber results showed that overall retention was commonly doubled by 
maximum spray wetting. Readily wetted and fairly flat bean-leaf surfaces that 
accumulate droplets retained up to 15 times as much sand when spray wetted as 
before treatment. Since, when leaves dry, much of the sand pattern approxi- 
mates that of the evaporated droplets, it is clear that the excess retention by wet 
surfaces depends largely on the area and depth of surface moisture that a leaf 
can retain and support. 

Under the stable conditions of the enclosed chamber, it was also possible to 
use a grain crop at several growth stages to observe retention efficiency of the 
developing stand. The increasing stem-to-leaf ratio with growth was manifested 
as lowered specific retention for barley. 



RETENTION OF NEAR-IN FALLOUT BY CROPS 407 




Fig. 1 Simulated-fallout exposure chamber. 



408 



LOVAAS AND JOHNSON 




Fig. 2 Microplot of grass in exposure chamber. 



For the field studies circular plots 20 ft or more in diameter were fitted with 
greased disk imp actors to monitor deposition (Fig. 3). The simulant was 
dispersed over a field plot from an elevated platform by means of a blower 
(Fig. 4). The actual release took place over a period of from 5 to 50 min 
depending on the stability of wind direction. Crop clippings taken at intervals 
over a 2-week period after contamination were counted by gamma spectrometry 
to reveal the retention functions (Fig. 5). Crops of eastern Colorado that were 
tested are alfalfa, corn, irrigated pasture bromegrass, sudan grass, sugar beets, 
and barley. 

Table 1 gives the conditions for the experiments of the 1969 crop year. 
Experimental results for two crop years are shown in Tables 2 to 6 and Figs. 6 
and 7. 



RESULTS AND DISCUSSION 



Table 2a gives measured initial retention of near-in simulant on field crops. 
In most cases neither particle size nor loading in the ranges tested was important 
compared with the retention differences characteristic of the target species. Bulk 
contamination of alfalfa is typically 5 to 10%. Contamination of pasture grass 
under dry, windy exposure conditions is contrasted with much higher initial 



RETENTION OF NEAR-IN FALLOUT BY CROPS 



409 




o 
a 

u 

-5 



bo 



410 



LOVAAS AND JOHNSON 




Fig. 4 Gas-powered blower on dispersal tower. 



retention under heavy dew. Retention by sudan grass is intermediate to that by 
bromegrass and corn. Bulk contamination of corn (Table 2b) was not highest 
even though it retained most sand as a percent of ground-area deposition. Initial 
retention of 88- to 175-ju sand by sugar-beet tops (40%) was markedly higher 
than retention of 175- to 350-jU sand (4%). Retention was calculated on a 
plant-area basis rather than a ground-area basis for sugar beets only. 

Table 3 shows weathering half-time of external contamination. The sand is 
lost from alfalfa with a half-time of about 1 week. Heavily laden pasture grass 
exposed under heavy dew had a 1-day half-time for about 3 days, after which 
further loss was barely detectable over 2 weeks. Young 2.5-ft-tall corn lost half 
of its simulated fallout in 6.5 days, whereas a more nearly mature 8-ft stand had 
a half-time of about 2 weeks. Weathering from sugar-beet tops proceeded with a 
half-time of 3 to 5 days for fine sand but was negligible for coarse sand, which 
was already at a low bulk level because of poor initial retention. 



RETENTION OF NEAR-IN FALLOUT BY CROPS 



411 




Fig. 5 Clipping of alfalfa within sampling ring. 



412 



LOVAAS AND JOHNSON 



Table 1 

SUMMARY OF SECOND-CROP-YEAR EXPERIMENTAL RELEASES 
ON FIELD CROPS 















Distance from 










Length of 


Sand 


blower to plot 


Experiment 


Crop 


Date 


Time 


experiment, days 


size* 


center, ft 


1 


Alfalfa 


6/24 


1400 


3 


L 


15 


2 


Alfalfa 


6/26 


1100 


11 


S 


30 or 45 


3 


Corn 


7/08 


1630 


24 


L 


30 


4 


Corn 


7/08 


1715 


24 


S 


30 


5 


Barley 


7/10 


1710 


17 


L 


25 


6 


Barley 


7/11 


1120 


18 


S 


20 


7 


Sugar beets 


7/29 


1930 


19 


S 


50 


8 


Sugar beets 


7/30 


1145 


19 


L 


50 


9 


Corn 


8/05 


0935 


16 


L 


20 


10 


Corn 


8/05 


1040 


16 


S 


20 


11 


Bromegrass 


8/07 


1030 


18 


L 


40 to 50 


12 


Bromegrass 


8/08 


1600 


17 


S 


40 to 50 


13 


Alfalfa 


8/19 


1505 


15 


S 


30 


14 


Alfalfa 


8/19 


1620 


15 


L 


30 


15 


Alfalfa 


8/26 


1140 


10 


S 


30 


16 


Alfalfa 


8/28 


1230 


10 


L 


25 


17 


Bromegrass 


9/11 


0720 


15 


S 


15 to 20 


18 


Bromegrass 


9/11 


0815 


15 


L 


25 


19 


Sudan grass 


9/16 


1539 


13 


S 


25 


20 


Sudan grass 


9/17 


1500 


12 


L 


25 



'Abbreviations are L, large (175 to 350 m); and S, small (88 to 175 n). 



Figure 6 shows retention of 88- to 175-jU sand by an alfalfa plot. Figure 7 is 
another retention function, this time for irrigated pasture bromegrass. Both 
figures show step changes caused by rainstorms. Table 4 summarizes data on 
removal of sand by rainstorms. These limited data do not quantitate a relation of 
percent of loss to inches of rainfall. It is clear that the small amount of coarse 
sand retained initially is less disturbed by rain. Table 5 expresses wind 
weathering of sand from the crops as the product of half-time and average wind 
speed. 

Table 6a shows the approach to assay of distribution of sand on plant parts. 
Only corn, barley, and sugar beets were sampled in this way. Table 6b indicates 
that corn initially held 10 to 20% of its fine sand and 50% of its coarse sand on 
leaves. At 9 days the figures were 5 to 10% for fine sand and 2 to 3% for coarse 
sand. On corn that had 14 to 18 segments, initial retention had broad maximums 
on descending segments 3 to 6 for 88- to 175-/J sand and segments 7 to 10 for 
175- to 3 50-fJL. At 16 days the maximum was indistinct for fine sand but had 



RETENTION OF NEAR-IN FALLOUT BY CROPS 



413 



Table 2a 
INITIAL RETENTION OF EXTERNAL CONTAMINATION 





Wind, 
mph 


Moisture 


Sand 
size* 




Initial retention 


Experiment 


% 


m 2 /kg, wet 


m 2 /kg, dried 








Alfalfa 








2 


12 to 30 




S 


2 


0.008 


0.045 


13 


6 




S 


6.5 


0.07 


0.45 


15 


to 10 




S 


17 


0.12 


0.8 


wa 


None 


Trace rain 


S 


23 






wb 


to 20 




s 


7.2 






1 


4 


Dew 


L 


15 


0.075 


0.65 


14 


6 




L 


3 


0.02 


0.17 


16 


2 to 10 




L 


6 


0.05 


0.25 


wc 


None 


B 


L 

rome grass 


5 






12 


6 




S 


4.5 


0.065 


0.3 


17 


1 to 2 


Heavy dew 


S 


100 


1.2 


6 


wf 


None 




S 


7.4 






11 


7 




L 


0.4 


0.0075 


0.04 


18 


None 


Heavy dew 


L 


85 


0.8 


3.5 


wg 




Trace rain 

Si 


L 

jdan Grass 


5.5 






19 


2 to 4 




S 


8.5 


0.08 


0.4 


20 


2 to 4 




L 


7.5 


0.05 


0.25 



Abbreviations are S, small (88 to 175 ju); ar >d L, large (175 to 3 50 ju). 



been sharpened for the coarse sand by loss from top segments. Barley heads 
(Table 6c) lost coarse sand to a noticeably greater extent in 17 days than did 
stems. Sugar-beet tops displayed a similar transfer from top to plant base for 
both sizes of sand. 

Although it is not the intent of our project to engage in beta-dose 
calculations, we will briefly describe the manner of the use of our data for that 
purpose. Bulk contamination level, integrated over time, may yield total dose 
when related to other measurements on the radiations from particles in a given 
fallout field. Where meristematic or vegetative sensitivity warrants, adjusted 
local- structure excess beta dose based on distribution of retention at that 
location may be related to the radiation emission of sized particles, to the 
self-absorption by aggregations of particles, and to dose exchange among 
contaminated plant structures. 



414 

Table 2b 
INITIAL RETENTION OF EXTERNAL CONTAMINATION 



Wind, Sand 



Initial retention 



Experiment mph Moisture size* % m 2 /kg, wet m 2 /kg, dried 

Corn 



4 


to 15 


10 


2 


wd 




3 


to 10 


9 


2 


we 





S 


15 


0.25 


2.5 


S 


35 


0.1 


0.65 


s 


44 






L 


15 


0.25 


2.5 


L 


35 


0.1 


0.65 


L 


32 







Barley 



to 1 


S 5.8 


0.04 


0.1 


1 to 2 


L 5.8 
Sugar Beets 


0.04 


0.1 


4 


Drizzle S 40 


0.25 


3 


7 


H 2 drops L 4 


0.015 


0.2 



* Abbreviations are S, small (88 to 175 ju); and L, large (175 to 3 50 m). 

Table 3 
WEATHERING TIME OF EXTERNAL CONTAMINATION 





Experiment 


Half- 


time, days 


Retainer 


88- to 175-M sand 


175- 


to 350-ju sand 


Alfalfa 


2, 1 


10 


Experiment cut short 




13, 14 


7 




7 




15, 16 


6 




6 


Bromegrass 


12, 11 
17, 18 


1 day for 3 days, 
then 19 days 

1 day for 3 days, 
then flat* for 
both sand sizes 




14 


Sudan grass 


19, 20 


9.5 




Flat* 


Corn 


4, 3 


6.5 




6.5 




10, 9 


12 




12 


Barley 


6, 5 


11 




11 


Sugar beets 


7, 8 


3, before rain 
5, after rain 




Flat* 



"Curve is relatively flat; half-time appears to be infinite. 



RETENTION OF NEAR-IN FALLOUT BY CROPS 



415 



100 



10 



0.1 



: d 


I 

D 


I I I 


1 


1 1 1 1 1 


I I 


I 


- 


- 




D 


D 


D 






- 


: * 


« 






D 










1 


- 




1 


K 


* 

* 






D 


D 


- 


I 


I 


Rain, 0.55 in. 

1 1 1 


1 


Rain, 0.17 in. 

! I I 1 


I 


Rain, 


X 
W 

0.61 in. 

I I 


X 

W 


- 



4 6 8 10 

DAY OF EXPERIMENT 



12 



14 



16 



Fig. 6 Retention of 88- to 17 5-jU sand by a plot of alfalfa. X, percent 
retention; D, m 2 /kg, dried, xlOO; W, m 2 /kg, wet, xlOO. 





-D 


I I 


I I 


I I 


I I 


I I I 


Mill 






X 










- 


10 


W 


D 
W 


X 

D 


X 

D 


X 

D 


X 

D 


— 








W 


W 


W 


W 


X 


1 

n 1 


I 


I I 


I I 


I I 


I I 


I I I 1 


D — 

w 
Rain, 0.47 in. 



4 6 8 

DAY OF EXPERIMENT 



14 



Fig. 7 Retention of 88- to 175-ju sand by a p!ot of irrigated pasture 
bromegrass. X, percent retention; D, m 2 /kg, dried, xlO; W, m 2 /kg, wet, xlO. 



416 



LOVAAS AND JOHNSON 



Table 4 
RAIN WEATHERING OF SAND FROM CROPS 



Median retention, 



88- to 175-ju sand 



175- to 350-ju sand 



Crop 



Length of Before After Before After 

experiment, days Rain, in. weathering weathering weathering weathering 



Alfalfa 

Bromegrass 
Sudan grass 

Corn 



3 
10 

10 

5 



Barley 4 

Sugar beets 5 



0.77 





1.2 


0.47 


8 


0.47 


6 


0.25 and 


8.5 


hail 




0.25 and 


* 


hailt 




0.38 


20 



0.6 

3 
4 



10 



*Little effect. 
tPart of fields. 



Table 5 
WIND WEATHERING OF SAND FROM CROPS 





Number of 






Half-time 






Crop 


monitored 
releases 


Sand 


size* 


(T/2), 
days 


MPH* 


T/2 x MPHt 


Alfalfa 


2 


S 












2 


L 




6.5 


2.2 


14.3 


Bromegrass 


2 
2 


S 
L 




1, 19 
l,flati 


2.2 


2.2, 41.8 
2.2, large 


Sudan grass 


1 


S 




9.5 


1.8 


17.1 




1 


L 




Flat$ 




Large 


Corn 


2 


s, 


L 


6.5 


1.2 


7.8 




2 


s, 


L 


>12 


3.9 


>46.8 


Barlev 


1 


s 












1 


L 




11 


1.8 


19.8 


Sugar beets 


1 
1 


s 

L 




4 
Flat$ 


3.2 
3.2 


12.8 
Large 



* Abbreviations are S, small (88 to 175 M);and L, large (175 to 3 50 m). 

tMPH is average wind speed. 

±Curve is relatively flat; half-time appears to be infinite. 



Table 6a 

SAMPLING OF DISTRIBUTION OF SAND 
ON PLANT PARTS 

Crop Localization distribution 

Corn Two-segment lengths, stem and leaf 

Stems with leaf angles vs. bodies of leaves 
Barley Heads vs. stems 

Beet Tops vs. bases 

Alfalfa Not fractionated 

Bromegrass Not fractionated 



Table 6b 
REDISTRIBUTION OF SAND ON CORN BY WEATHERING 

Sand size, ju Experiment Retention 

Segmental Distribution on 14-Segment Stalks 

88 to 175 10 Broad maximum (2 x top segments), 

maximum 3 to 6 segments from top 
175 to 3 50 9 Broad maximum (3 x top segments), 

maximum 7 to 10 segments from top 

Leaf Vs. Leaf + Stem with Leaf Angle 

Start 9 days 

88 to 175 10 0.2 0.03 

4 0.1 0.02 

175 to 350 9 0.5 0.05 

3 0.5 0.1 



Table 6c 
REDISTRIBUTION OF SAND BY WEATHERING 



Retention, fraction 
Sand size, u Experiment Initial 17 days 19 days 

Barley, Heads Vs. Heads + Stems 



417 



88 to 175 


6 0.8 0.7 




175 to 350 


5 0.9 0.3 
Sugar Beets, Tops Vs. Tops + Base 




88 to 175 


7 0.9 


0.1 


175 to 350 


8 0.2 


0.03 



418 LOVAAS AND JOHNSON 

SUMMARY 

We have presented data on initial retention and weathering of simulated 
near-in fallout particles from alfalfa, corn, barley, irrigated pasture bromegrass, 
sudan grass, and sugar-beet tops. Initial retention of the particles ranged from 
complete to practically no retention, depending on weather conditions at the 
time of exposure and on the plant structure. Observed weathering half-times 
were from 1 day or less to more than 2 weeks. The data may be applied to 
calculate bulk contamination of forage and radiation dose to growing plants. 

ACKNOWLEDGMENTS 

This study is supported by the Office of Civil Defense under contract 
DAH20-68-C-0120. D. W. Wilson was the original principal investigator of the 
project. 



REFERENCES 

1. S. L. Brown and V. F. Pilz, U. S. Agriculture: Potential Vulnerabilities, SRI Project No. 
MU-6250-052, Stanford Research Institute, January 1969. 

2. M. C. Bell and C. V. Cole, Vulnerability of Food Crop and Livestock Production to 
Fallout Radiation, USAEC Report TID-24459, UT-AEC Agricultural Research Labora- 
tory, Sept. 7, 1967. 

3. C. F. Miller, Operation Ceniza-Arena: The Retention of Fallout Particles from Volcan 
Irazu (Costa Rica) by Plants and People. Part III, Report AD-673202, Stanford Research 
Institute, December 1967. 

4. G. M. Dunning, Health Aspects of Nuclear Weapons Testing, USAEC Report TID-20723, 
U. S. Atomic Energy Commission. 

5. D. E. Clark and W. C. Cobbin, Some Relationships Among Particle Size, Mass Level, and 
Radiation Intensity of Fallout from a Land Surface Nuclear Detonation, Report 
USNRDL-TR-639, Naval Radiological Defense Laboratory, Mar. 21, 1963. 

6. W. 6. Lane, Fallout Simulant Development, Final Report to OCD, Stanford Research 
Institute, September 1969. 



PREDICTION OF SPECIES RADIOSENSITIVITY 



HARVEY L. CROMROY, RICHARD LEVY, ALBERTO B. BROCE, and 
LEONARD J. GOLDMAN 

Departments of Entomology and Radiology, Division of Nuclear Sciences, 
University of Florida, Gainesville, Florida 



ABSTRACT 

A study was made on the feasibility of using the mammalian columnar epithelial cell of the 
duodenum and the insect endothelial cell of the midgut as biological indicators of radiation 
sensitivity. Thirty species of mammals and twenty species of insects were used. Data 
demonstrating situations where the respective cells would be most useful as parameters for 
radiosensitivity are presented. 



The major aim of our research was to determine biological indicators that could 
serve as predictors of radiation sensitivity. 

Previous research by Sparrow and co-workers 1 established that the 
radiosensitivities of plants to ionizing radiation could be predicted on the basis 
of a regression line measured by the interphase chromosome volume (ICV) 
against the lethal dose required to kill 50% of a given population (LD 50 ) for 
established irradiated species. The ICV was defined as the nuclear volume of a 
cell divided by the diploid chromosome number of the species. Conger, 4 who 
initiated this research project, further substantiated this hypothesis with his 
work on Florida gymnosperms. We began our research to determine whether 
this type of correlation also exists in insects and mammals. The biological- 
indicator cells, selected because of their established sensitivity to ionizing 
radiation, were the endothelial cells lining the midgut of insects and the 
columnar epithelial cells of the duodenal intestinal mucosa of mammals. 

The initial publication was on seven species of mammals and eight species of 
insects. 5 At that time it was reported that the mammalian species studied had a 
slope with a positive declination, whereas the insects had a negative declination 
to the slope conforming with Sparrow's previous work. Simply, the mammalian 



419 



420 



CROMROY, LEVY, BROCE, AND GOLDMAN 



slope indicated that the larger the ICV, the less sensitive the animal was to 
ionizing radiation; the inverse relation holds true for insects and plants. Later 
research amplified the data to include 22 species of mammals and 11 species of 
insects. We found contradictions within the mammals, in the rodent species in 
particular, which presented a number of problems. 

Our current data on 20 species of insects and 30 species of mammals are 
presented here. For purposes of clarity this paper is subdivided into two 
sections; the first deals with mammals and the second with insects. 

MAMMALS 

The order Rodentia presented so much scatter when included with the other 
orders of mammals that we arbitrarily lumped all rodent data together. 

Mammals Other Than Rodents 

The data in Fig. 1 are for the midline air dose in roentgens with a 1-MVp 
X-ray unit. The LD50S, except the one for sheep, were done at the Naval 
Radiological Defense Laboratory, San Francisco, Calif., by Ainsworth et al. 6 
The data on sheep were obtained through the cooperation of the Radiobiology 
Laboratory, Biophysics Branch, Air Force Weapons Laboratory, Kirtland Air 



900 



700 — 



6 500 

ro 

o 
in 
Q 



300 



100 



I I ! 


I I I 


i i • 

Rabbit y 


Y = 73.8X + 203 
r = + 0.93 






— 


Monkey • ^r 


— 


Cowar 
Goat^Xs™™ 


• Man 
• Sheep 





Dog«/^ 




— 


I I I 


I I I 


i I 



2.0 



4.0 
ICV,jLl 3 



6.0 



8.0 



Fig. 1 Relation of interphase chromosome volume to LD50/30 exposure dose 
(midline air dose with 1-MVp X ray) in mammals other than rodents. 



PREDICTION OF SPECIES RADIOSENSITI VITY 



421 



Force Base, N. Mex. The regression equation, or predictor formula, is 
Y = 74X + 203, where Y is LD50/30 days m roentgens, midline air dose, and X 
is ICV. The coefficient of correlation, r, is +0.93, where r indicates a linear 
relation between points. If r equals ±1, a perfect correlation exists. A high value 
for r indicates that this is an excellent predictor for X radiation and exposure 
considerations only. 



Rodents 

Figure 2 presents an analysis of 1 1 species of rodents. The ICV's presented 
are the average of the male and female of the species, and the LD 50 /3o's were 
taken from the literature. 7 13 The three families of rodents represented are 
Muridae, Cricetidae, and Heteromyidae. The analysis of points by least squares 
has a slope equation of Y = 122X + 688, where Y is the LD 5 0/30 absorbed dose 



1200 — 



1000 



o 

§ 
J? 800 



600 — 



400 





I 

Y = 


I I I 
122X + 688 


I I • 
PFO 


— 


r = 


0.40 




— 




0. r- ppo 
PLE • 

• tMU 


^^ — 


— 




• RF ^T 

• MP S^ 




— 




S?^ P#M 


• RNO 


— 




<r #MM 


— 


— 






— 


— 






— 


— 


I 


• OP 

I I I 


I I 



0.5 



1.5 



3.5 



2 2.5 2 

ICV,/! 3 

Fig. 2 Relation of interphase chromosome volume to LD50/30 absorbed dose 
for rodent species. •, average ICV for male and female of species. 



MM, Mus musculus 
MP, Micro tus pinetorum 
MUfMeriones unguiculatus 
OP, Oryzomys palustris 
PFO, Perognathus formosus 
PLE, Peromyscus leu cop us 



PM, Peromyscus mamculatus 
PPA, Perognathus parvus 
PPO, Peromyscus polionotus 
RF, Mus musculus, RF strain 
RNO, Rattus norvegicus 



422 



CROMROY, LEVY, BROCE, AND GOLDMAN 



in rads from 60 Co and X is the ICV. The coefficient r is +0.40. This figure is 
strongly influenced by points OP and PFO. Removal of these two points would 
change the analysis considerably. 

Figure 3 is a graphical representation of the analysis of 13 different species 
of male rodents. The ICV's plotted are for males only. Again there is a positive 
declination to the slope and a high degree of scatter. The predictor equation is 
Y = 152X + 544, and r equals +0.46. 



1200 



1000 



S 800 



400 





I 

Y 


I I 
= 152X + 544 


I I I 






r 


= 0.46 






— 






• PLE 


— 


— 




RH 
MP # 
toiM C £ 


SH y^ 

yS #RNO 


— 


— 




MMt/ ,PPA 


— 


— 




• OP 




— 


— 


I 


• WA 
I I 


I I I 


— 



0.5 



1.5 



2 2.5 

ICV, Ai 3 



3.5 



Fig. 3 Relation of interphase chromosome volume of male rodent species to 
LD50/30 absorbed dose. 



CG, Cricetulns griseus 
MM,M//s musculus 
MP, Microtus pinetorum 
ON, Ochrotomys nuttalli 
OP, Oryzomys palustris 
PLE, Peromyscus lencopus 
PM, Peromyscus mamculatus 



PPA, Perognathus parvus 
RF, Mus musculus, RF strain 
RH, Reithrodontomys humilis 
RNO, Kattus norvegicus 
SH, Sigmodon bispidus 
WA, Rattus rattus, Wistar 
Albino strain 



Figure 4 pictures the analysis of 12 different female rodent species. There is 
a negative declination to the slope, indicating an inverse relation to the slope 
obtained with male rodents. In this case the predictor equation is 
Y = — 137X + 1102, and r is —0.46. Therefore the contribution from the male 
species is the factor that accounts for the positive slope obtained in Fig. 2. 



PREDICTION OF SPECIES RADIOSENSITI VITY 



423 



1200 



1000 



o 

CO 

in 800 
Q 



600 



400 



Y = -137X +1102 
r = -0.46 


— 


P i E #RF 

^S^ ©MP 
SD •>. 


— 


\^ .PPA*™ 




_ tMM\sW #RNO 


— 


^^ 


— 


— tMA 


— 


• OP 

I I I I I I 


— 



0.5 



1.5 



2 2.5 

ICV,/i 3 



3.5 



Fig. 4 Relation of interphase chromosome volume of female rodent species 
to LD50/30 absorbed dose. 



MA, Mesocricetus auratus 
MM, Mus musculus 
MP, Microtus pinetorum 
OP, Oryzomys palustris 
PLE, Peromyscus leucopus 
PM, Peromyscus maniculatus 
PPA, Perognathus parvus 
RF, Mus musculus, RF strain 



RNO, Rattus norvegicus 
SD, Rattus rattus, Sprague 

Dawley strain 
SW, Mus musculus, Swiss 

Webster strain 
WA, Rattus rattus, Wistar 

Albino strain 



Table 1 presents a comparison of male and female ICV's. The male almost 
always has a larger 1CV than the female, but the LD50/30 of the male may be 
larger or smaller than that of the female. This causes the poor predictive values 
for the species. 

Figure 5 compares Fry's data 14 on mean survival times for massive doses of 
whole-body irradiation with our ICV data. A negative slope is obtained, with 
Y = — 61X + 264 and r = —0.65 ; this indicates a much better correlation between 
points. If we combine Fry's data and those of Dunaway et al., 9 we obtain the 
slope shown in Fig. 6. In this case, Y = 0.40X + 215, and r equals —0.68. Table 2 
compares the observed and the predicted mean survival times (MST). This 
relation appears to be much more valid for predictive purposes. 



424 



TABLE 1 

COMPARISON OF MALE AND FEMALE RODENT ICV AND LD 50/30 









Observed 


Predicted 


Species 


Sex 


ICV 


LD5 0/3Q, rads* 


LD 50 /3 0, r adst 


Rattus norvegicus 


f 


2.88 


949 


707 




m 


3.07 


795 


1011 


Mus musculus 


f 


1.62 


802 


880 




m 


1.81 


851 


818 


Peromyscus leucopus 


f 


1.07 


1043 


955 




m 


2.50 


1091 


924 


Microtus pinetorum 


f 


1.30 


1004 


924 




m 


1.52 


883 


775 


Oryzomys palustris 


f 


2.04 


484 


823 




m 


2.02 


584 


848 



*Data are taken from Dunaway et al. 8 

tPredicted value is taken from either Fig. 3 or Fig. 4, depending on sex. 



250 



200 



> 

CE 
D 
c/) 

z 
< 

111 

^ 100 



50 



0.5 



i — r 



Y = -60.8X + 264 
r = -0.65 




MMt 



JL I L_J L 



1.5 



2 2.5 

ICV,^ 3 



3.5 



Fig. 5 Relation of interphase chromosome volume to mean survival time of 
mammals exposed to large doses of whole4)ody irradiation. 



CG, Cricetulus griseus 
CL, Chinchilla laniger 
MM, Mus musculus 



PLE, Peromyscus leucopus 
PLO, Perognathus longimemhris 
RNO, Rattus norvegicus 



PREDICTION OF SPECIES RADIOSENSITIVITY 



425 



220 



180 — 



140 



100 



60 





I I I 




I I I 
Y = -0.40X + 215 


— 






r = -0.68 — 




• PLO 




— 






— 


— 


MP#S. 




— 


— 




• OP 


— 




PLE» N 


V • CL 




RF* 









MMC* 


CG 


fcJ'LEcf 


— 






N*RNO — 


— 


I l 




• \ _ 

RN09 

III 



0.5 



1.5 



2 2.5 

ICV,M 3 



3.5 



Fig. 6 Relation of interphase chromosome volume to mean survival time of 
mammals exposed to large doses of whole-body irradiation. 



CG, Cricetulus grtseus 
CL, Chinchilla laniger 
MM, Mus muse id its 
MP, Micro tus pine to rum 
OP, Oryzomys palustris 



PLE, Peromyscus leu cop us 
PLO, Perognathus longimembris 
RF, Mus musculus, RF strain 
RNO, Rattus norvegicus 



Discussion of Results 

Table 3 summarizes the predictor equations and coefficients for Figs. 1 to 6. 
As can be seen, the slope for data from mammals other than rodents is the best 
predictor; its very high coefficient indicates a good degree of reliability. The 
work with LD 50 / 30 and ICV in rodent species is still unsatisfactory. The scatter 
plus the positive slope for the males vs. the negative slope for the females makes 
predictability inaccurate. Part of the problem is undoubtedly the fact that the 
LD50/30 data were taken from the literature, and consequently different dose 
rates were used to obtain the respective LD 50 / 30 's. It may well be that the new- 
formula suggested by Dunaway et al. 9 [Y = 20.75X — 2.77, where Y is rads per 
gram and X is red blood cell count/(27rr) intestine] may be one of the better 
rough predictors of LD 50 / 30 . 

Before the rodent data can have any validity as a predictor for LD 50 / 30 , 
much more study must be done on the parameters affecting the radiation 
sensitivity of the species. It appears that the use of the ICV for mean-survival- 
time predictions is good since this provides good estimates. 



426 



CROMROY, LEVY, BROCE, AND GOLDMAN 



TABLE 2 

COMPARISON OF MEAN SURVIVAL TIMES (MST) FOR LARGE DOSES 
OF WHOLE-BODY RADIATION WITH ICV IN RODENTS 



Species' 



ICV 



Observed 
MST, hr 



Predicted 
MST,hr 



Perognathus longimembns, average 
Peromyscus leucopus, male 
Peromyscus leucopus, average 
Cricetulus griseus, male 

Rattus norvegicus, male 
Mus musculus, male 
Chinchilla laniger, male 
Microtus pinetorum, average 

Oryzomys palustris, average 
Mus musculus, RF strain, average 
Rattus norvegicus, average 
Mus musculus, average 



1.95 


192 


136 


2.50 


112 


113 


1.80 


132 


142 


2.28 


118 


122 


2.88 


82 


98 


1.80 


115 


142 


2.35 


128 


119 


1.41 


154 


157 


2.03 


144 


132 


1.95 


122 


136 


2.98 


98 


94 


1.71 


139 


145 



*The term "average" after species indicates that the ICV given is the 
average of the values for the male and female of the species. 



TABLE 3 

SUMMARY OF THE PREDICTOR EQUATIONS AND THEIR 
COEFFICIENTS FOR FIGS. 1 TO 6 



Figure 



Predictor 



Coefficient 



Fig. 1, Mammals other than rodents 
Fig. 2, ICV with LD 5 q in rodents 
Fig. 3, ICV with LD50 in male rodents 

Fig. 4, ICV with LD50 in female rodents 
Fig. 5, MST with ICV 
Fig. 6, MST with ICV 



Y = 73. 8X + 203 


r = +0.93 


Y = 122X + 688 


r = +0.40 


Y = 152X + 544 


r = +0.46 


Y = -137X + 1102 


r= -0.46 


Y = -61X + 264 


r = -0.65 


Y = -40X + 215 


r = -0.68 



INSECTS 



Our initial studies on insects were done with 11 species. The LD 50 was taken 
for 24 hr and the biological indicator cell was the endothelial cell lining the 
midgut. A 24-hr period was selected on the basis of the large variation in 
life-spans of insects and the requirements of culture rooms for sustained 
life-history studies. The 11 species studied gave a predictor formula of 
Y = 2.67X + 163.42, where Y is LD 50 /2 4 hr in roentgens and X is the ICV. 



J 



PREDICTION OF SPECIES RADIOSENSITIVITY 



427 



Figure 7 presents a graphical analysis of 17 species of insects, the majority of 
which were irradiated with 60 Co at identical dose rates with three replications 
per point for verification of LD 50 . All insects were in the adult stage and were 
of the orders Coleoptera, Diptera, Orthoptera, Hemiptera, Homoptera, and 
Anoplura. There is a negative declination to the slope; Y equals — 4.06X + 184, 
and r equals —0.46. This agrees with Sparrow's data 3 indicating that the larger 



260 



o 

in 
Q 



140 



80 



20 



I 

"•TCA 


I 


III! 


I I I I I 

Y = -4.06X + 184 
r = -0.46 


— •TM 






— 


Tph 


• OS 


• so 


— 


■*TCO 




""""***^>^«^ #NC 

PF ^^^^ 
• BG 


LM 
^••SC 

— -^^; d 


I 


• PA 
I 


• AD •BB 

I I I I 


i i i i i 



13 17 

ICV,/U 3 



21 



25 



Fig. 7 Relation of interphase chromosome volume of 17 species of insects to 



LD 



5 0/24 



Ml 



h r exposure dose ( Co irradiation) 



AD, Acbeta domestica 

BB, Brevicoryne brassicae 

BG, Blatella germanica 

CL, Cimex lectularis 

LM, Leucophaea maderae 

MD, Musca domestica 

NC, Nauphoeta ctnerea 

OS, Oryzaephilus surinamensis 

PA, Periplaneta americana 



PE, Prodenia eridenia 

PF, Periplaneta fuliginosa 

PH, Pediculus humanus bumanus 

SC, Stomoxys calcitrans 

SO, Sitopbilus oryzae 

TCA, Tribolium castaneum 

TCO, Tribolium confusum 

TM, Tenebrio molitor 



the ICV, the more sensitive the insect species is to ionizing radiation. In Fig. 8 
the Orthopteran species are analyzed separately. Note that a positive slope is 
obtained; however, r is +0.12, indicating a very poor linear relation between 
points. For the Coleopteran species, Fig. 9, nuclear volume is plotted against 
LD 50 / 2 4 hr because so few chromosome numbers are available for many of the 
beetles. A negative, declining slope is obtained, and r equals —0.27. This is also a 



428 



CROMROY, LEVY, BROCE, AND GOLDMAN 



150 




I 

Y = 6.4X + 1.3 
r = 0.12 


l l 

• NC 


I 


^r 










A\M 




110 










— 








• BG yS 




PF< 


70 










— 


?n 




• PA yf 


• AD 
I I 


I 


— 



10 15 

ICV,jU 3 



20 



25 



Fig. 8 Relation of interphase chromosome volume of Orthopteran species to 
LD50/24 hr exposure dose. 



AD, Acheta domestica 
BG, Blatella germanica 
LM, Leucopbaea maderae 



NC, Nauphoeta cinerea 
PA, Periplaneta americana 
PF, Periplaneta fuliginosa 



poor indication of linear relation between points. Plotting the dose required to 
reduce the life-span of the insect species by one-half under laboratory conditions 
against the ICV gives the curve shown in Fig. 10. The predictor equation is Y = 
— 0.73X + 11.04, where Y is dose in kiloroentgens required to reduce life-span 
50%. In this case r is —0.72; this indicates a high linear relation between points, 
and good predictive values are obtained. The dose data used in Figs. 10 and 11 
are extrapolated from a series of research reports by other workers. 15 " 21 Fig- 
ure 11 compares LD 50 /2 8 days m kilorads and ICV. The predictor equation is 
Y = — 0.89X + 12, where Y is LD 5 0/2 g day dose in kilorads and r is —0.82. 



Discussion of Results 



LD 



The data on insects appear to be best when either life-span shortening or 
so/28 days i s considered. In all probability the life-span shortening parameter 
will turn out to be best since there is such considerable variation in insect 
life-spans; for example, the American cockroach 15 has a life-span of approxi- 
mately 400 days under laboratory conditions, whereas the house fly 16 has a 
life-span of only 25 days. The overall graph of 17 species is not so good a 



PREDICTION OF SPECIES RADIOSENSITI VITY 



429 



300 — 



o 
in 
Q 



100 





I I I 

• TCA 


I 


I I 


I I I 
Y = -0.33X + 217 










r = -0.27 — 


— 


• TM 






— 


— 




• OS 


• LS 


• SO — 


— 


• TCO 


• GP 




— 


— 




• MA 




— 


— 


I I I 


I 


I I 


i i i 



40 80 1 20 

NUCLEAR VOLUME,/! 3 



160 



200 



Fig. 9 Relation of nuclear volume of Coleopteran species to LD50/24 hr 
exposure dose. 



GP, Gibbium psylloides 
LS, Lasioderme serricorne 
MA, Mezium americanum 
OS, Oryzaephilus surinamensis 



SO, Sitophilus oryzae 
TCA, Tribolium castaneum 
TCO, Tribolium confusum 
TM, Tenebrio molitor 



predictor as was expected; there are several explanations for this, however. 
Preliminary cytogenetic investigations by several authors 19,20 showed the 
existence of unique chromosome structures in different orders of insects, such as 
chromosomes with diffuse centromeres or polycentric chromosomes (i.e., each 
chromosome has more than one region for spindle fiber attachment). If 
polycentric chromosomes are subjected to ionizing radiation, the chromosome 
fragments produced will very likely possess at least one centromere and thus 
could function as independent chromosomes; this would reduce the probability 
of lethal mutations. The rate of deoxyribonucleic acid turnover in the midgut is 
another factor since the true plant feeders may differ considerably from the seed 
and grain feeders as well as from the blood feeders. Since the mechanisms by 
which radiation produces mortality in insects are still largely undetermined, 
selection of the proper parameter as an end-point measurement of radiation 
sensitivity presents many problems. A number of other parameters that have 
been used in estimating radiosensitivity of insects include: 

1. Body weight. The larger the insect, the lower the dose required to kill. 



430 



CROMROY, LEVY, BROCE, AND GOLDMAN 



14 



12 



LU 10 

w 

O 

Q 



§ 6 



.< 4 — 





I 

• TCA 


I 


i i 


— 




• OS 


Y = -0.73X+ 11.04 
r = -0.72 




TCO ^^ 






— 


• TM 




^^ — 


— 


I 


• PA 

JL 


^v*. BG 

^*# AD 

I I 



2.Z> 



5.0 7.5 

ICV,^3 



10 



12.5 



Fig. 10 Relation of insect interphase chromosome volume to LD50/28 day 
dose. 



AD, Acbeta domestica 

BG, Blatella germanica 

OS, Oryzaephilus surmamensis 

PA, Periplaneta americana 



TCA, Tribolium castaneum 
TCO, Tribolium confusum 
TM, Tenebno molitor 



2. Phylogenetic relations. 

3. Physical activity. This is a difficult parameter to quantify. 

4. Life-span. Longer-living insects are supposed to be more sensitive to 
ionizing radiation. 

We believe that the best predictor formula will probably be a combination of 
several of these parameters combined with interphase nuclear volume. 

SUMMARY 

Mammalian species other than rodents provide the best predictor slope for 
LD50/30 exposure doses. The interphase chromosome volume for rodents is 
useful as a predictor only when we are dealing with the gastrointestinal form of 
death measured in mean survival time. The amount of scatter in rodent species 
obtained with the ICV's makes them questionable as the sole predictor sources 
for LD 50 /3o- 



_ 



PREDICTION OF SPECIES RADIOSENSITI VITY 



431 



14 



12 



10 



> 

(0 

■o 

00 
CM 

O 

in 
Q 



• TCA 



Y = -0.89X + 1 1 .82 
r = -0.82 




• PA 



12.5 



ICV,ju3 

Fig. 11 Relation of interphase chromosome volume of insects to mean 
mortality expressed as kilorad dose required to reduce life-span by one-half. 



AD, Acbeta domestica 

BG, Blatella germanica 

OS, Oryzaephilus surtnamensis 

PA, Periplaneta americana 



SO, Sitophilus oryzae 
TCA, Tribolium castaneum 
TCO, Tribolium confusum 



The interphase chromosome volume serves as a good predictor when we are 
considering LD 50 /2 8 days or mean mortality in insects. It is not so good when 
we are dealing with LD 5 /2 4 hr- 

ACKNOWLEDGMENTS 

This research was supported by the Office of Civil Defense. 

Many of the specimens used were obtained through the cooperation of Paul 
Dunaway, Ecological Sciences Division, Oak Ridge National Laboratory; T. J. 
O'Farrell, Battelle— Northwest; R. J. M. Fry, Argonne National Laboratory; 
Norman French, Laboratory of Nuclear Medicine and Radiation Biology, 
University of California; and M. Kinsella, Veterinary Sciences Division, Univer- 
sity of Florida. 



REFERENCES 

1. A. H. Sparrow and H. T. Evans, Nuclear Factors Affecting Radiosensitivity. I. The 
Influence of Nuclear Size and Structure, Chromosome Complement, and DNA Content, 



432 CROMROY, LEVY, BROCE, AND GOLDMAN 

in Fundamental Aspects of Radiosensitivity, Report of a Symposium, June 5 — 7, 1961, 
Upton, N. Y., USAEC Report BNL-675, pp. 76 — 100, Brookhaven National Laboratory, 
1961. 

2. A. H. Sparrow, L. A. Schairer, and R. C. Sparrow, Relationship Between Nuclear 
Volume, Chromosome Numbers, and Relative Radiosensitivities, Science, 141: 163 — 166 
(1963). 

3. A. H. Sparrow, A. G. Underbrink, and R. C. Sparrow, Chromosomes and Cellular 
Radiosensitivity. 1. The Relationship of Dq to Chromosome Volume and Complexity in 
Seventy-Nine Different Organisms, Radiat. Res., 32: 915-945 (1967). 

4. A. D. Conger and H. L. Cromroy, Radiosensitivity and Nuclear Volume in the 
Gymnosperms, Report OCD-PS-64-69, Office of Civil Defense, University of Florida, 
1966. 

5. H. L. Cromroy, Cellular Response to Radiation, Report TRC-67-40, Office of Civil 
Defense, University of Florida, 1967. 

6. E. J. Ainsworth, N. P. Page, J. F. Taylor, G. F. Leong, and E. T. Still, Dose-Rate Studies 
with Sheep and Swine, in The Proceedings of a Symposium on Dose Rate in Mammalian 
Radiation Biology, Apr. 29-May 1 1968, Oak Ridge, Tenn., D. G. Brown, R. G. Cragle, 
and T. R. Noonan (Eds.), USAEC Report CONF-680410, pp. 4.1-4.21, UT-AEC 
Agricultural Research Laboratory, July 12, 1968. 

7. W. F. Belk and A. E. Gass, Jr., Relative Resistance of Gerbils and Rats to Acute 
Cobalt-60 Irradiation, Report SAM-TR-69-16, School of Aerospace Medicine, Brooks 
AFB, Texas, 1969. 

8. P. B. Dunaway, L. L. Lewis, L. D. Story, J. A. Payne, and J. M. Inglis, Radiation Effects 
in the Soricidae, Cricetidae, and Muridae, in Symposium on Radioecology, Proceedings 
of the 2nd National Symposium May 15 — 17, 1967, Ann Arbor, Mich., D. J. Nelson and 
F. C. Evans, (Eds.), USAEC Report CONF-670503, pp. 173-184, AEC Division of 
Biology and Medicine and Ecological Society of America, March 1969. 

9. P. B. Dunaway, J. T. Kitchings III, J. D. Story, L. E. Tucker, and H. F. Landreth, in 
Health Physics Division Annual Progress Report for Period Ending July 31, 1969. 
USAEC Report ORNL-4446, pp. 63-65, Oak Ridge National Laboratory, October 
1969. 

10. F. B. Golley and J. B. Gentry, Response of Rodents to Acute Gamma Radiation Under 
Field Conditions, in Symposium on Radioecology, Proceedings of the 2nd National 
Symposium May 15 — 17, 1967, Ann Arbor, Mich., D. J. Nelson and F. C. Evans, (Eds.), 
USAEC Report CONF-670503, pp. 166-172, AEC Division of Biology and Medicine 
and Ecological Society of America, March 1969. 

11. Thomas P. O'Farrell, Effects of Acute Ionizing Radiation in Selected Pacific Northwest 
Rodents, in Symposium on Radioecology, Proceedings of the 2nd National Symposium, 
May 15-17, 1967, Ann Arbor, Mich., D.J. Nelson and F. C. Evans, (Eds.), USAEC 
Report CONF-670503, pp. 157-165, AEC Division of Biology and Medicine and 
Ecological Society of America, March 1969. 

12. W. H. Pryor, Jr., W. G. Glenn, and K. A. Hardy, The Gamma Radiation LD 50 (3o^ f° r 
the Rabbit, Radiat. Res., 30: 483-487 (1967). 

13. J. E. Traynor and E. I. Still, Dose Rate Effect on LD50/30 i n Mice Exposed to 
Cobalt-60 Gamma Irradiation, Report SAM-TR-68-97, School of Aerospace Medicine, 
Brooks AFB, Texas, 1968. 

14. R. J. Michael Fry, A. B. Rieskin. W. Kisieleski, A. Sallese, and E. Staffeldt, in 
Comparative Cellular and Species Radiosensitivity, V. P. Bond and T. Sugahara (Eds.), 
pp. 255-268, Igaku Shoin Ltd., Tokyo, 1969. 

15. M. M. Cole, G. C. La Breque, and G. S. Burden, Effect of Gamma Radiation on Some 
Insects Affecting Man, J. Econ. Entomol, 52: 448-450 (1959). 



PREDICTION OF SPECIES RADIOSENSITI VITY 433 

16. J. M. Cork, Gamma-Radiation and Longevity of the Flour Beetle, Radiat. Res., 7: 
551-557 (1957). 

17. P. B. Cornwell (Ed.), The Entomology of Radiation Disinfestation of Grain, pp. 1-17, 
119 — 141, Pergamon Press, Inc., New York, 1966. 

18. E. F. Menhinick and D. A. Crossley, Jr., A Comparison of Radiation Profiles of Acheta 
domestica and Tenebrio molitor, Ann. Entomol. Soc. Amer., 61: 1359-1365 (1968). 

19. E. F. Menhinick and D. A. Crossley, Jr., Radiation Sensitivity of Twelve Species of 
Arthropods, A nn. Entomol. Soc. Amer., 62: 711-717 (1969). 

20. D. T. North and G. G. Holt, in Isotopes and Radiation in Entomology, Symposium 
Proceedings, Vienna, 1967, pp. 391—403, International Atomic Energy Agency, Vienna, 
1968 (STI/PUB/166). 

21. E. W. Tilton, W. E. Burkholder, and R. R. Cogburn, Effects of Gamma Radiation on 
Rhyzopertha dominica, Sitopbilus oryzae, Tribolium confusum, and Lasioderma 
serricorne, J. Econ. Entomol., 59: 1363 — 1368 (1966). 

ADDITIONAL READING LIST 

Cromroy, H. L., Cellular Indicators of Radiosensitivity, OCD Report TRC-68-49, University 

of Florida, 1969. 
Cromroy, H. L., Mammalian Radiosensitivity, OCD Report TO-3140-(68), University of 

Florida, 1969. 



INSECT-INDUCED AGROECOLOGICAL 
IMBALANCES AS AN ANALOG 
TO FALLOUT EFFECTS 



VERNON M. STERN 

Department of Entomology, University of California, Riverside, California 



ABSTRACT 

Many species in the classes Insecta and Arachnida are phytophagous and compete with man 
and his domestic animals for food, and others attack man and animals directly or transmit 
plant and animal diseases. On the other hand, there are tremendous numbers of beneficial 
species; among them are plant pollinators, insects that aid in the decomposition and 
recycling of plant and animal debris, and thousands of other beneficial insects and mites 
that attack and kill the destructive species. Crop losses from insects amount to nearly 
$4 billion annually. Control measures (mainly chemicals) for crop protection in the field 
and for stored crop products cost nearly $750 million annually. Many insect-pest 
populations rise to damaging levels year after year in agroecosystems although this is rather 
uncommon in natural communities. The monoculture is a special type of agroecosystem 
resulting from man's technical efforts to control nature to meet his need for food and other 
products. It is somewhat doubtful whether we can change the monoculture into a more 
diversified agroecosystem despite the annual plagues of insect pests. Fallout radiation is 
somewhat similar to the pesticides that often cause ecological disruptions. Even though pest 
insects may be eliminated from certain areas by fallout radiation, they can be expected to 
become reestablished in these areas soon and again to compete with man for his food. For 
these and other reasons discussed, both beneficial and pest species will be important factors 
in food production in the event of nuclear war. 



During biological history four groups of organisms, reptiles, birds, mammals, and 
insects, have at some time during their evolution developed the power of true 
flight. Wings evolved but once and early in the evolutionary history of insects, 
and this ancestral pattern gave rise to the vast majority of present-day forms. 
Their ability to move rapidly from one area to another gives them a great 
flexibility and advantage in selecting suitable environments for survival, growth, 
and reproduction. 1 They also possess a great genetic variability that has 
permitted them to adapt to almost every conceivable habitat. Most species have 

434 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 435 

a high reproductive potential and produce several generations per year; this 
permits them to increase rapidly in numbers during the favorable season. 

Eighty-five percent of all insect species have complete metamorphosis, which 
permits specialization in different phases of their life history. Thus feeding and 
growth occur during the larval period; differentiation occurs in the pupal period; 
and mating, migration, and reproduction occur during the adult stage. Mobility, 
genetic variability, high reproductive potential, and complete metamorphosis 
have contributed greatly to the biological success of this diverse group of 
organisms. 

As a group insects are highly resistant to radiation, and many species have 
additional survival potential from fallout radiation because they spend a part of 
their life cycle protected in the soil, within plant tissue, within the plant debris 
near the soil surface, etc. 

There are about 2 million arthropod species. Many of those in the classes 
Insecta and Arachnida are phytophagous and compete with man and his 
domestic animals for food, and others attack man and animals directly or 
transmit plant and animal diseases. On the other hand, there are tremendous 
numbers of beneficial species. Some insects are plant pollinators; others aid in 
the decomposition and recycling of plant and animal debris; and, finally, there 
are thousands of predators and parasites that attack and destroy the destructive 
species. 2 For these and other reasons, both the destructive and the beneficial 
forms can certainly be considered important factors in the production of food in 
the event of nuclear disaster. 

This does not mean that insects are more important than fungi, bacteria, or 
viruses attacking plants and animals or that insects are more important than the 
hundreds of weed species competing with our commercial crops. The successful 
manipulation and control of all these organisms play important roles in 
high-quality and -quantity food production. 

Crop losses from pests amount to billions of dollars each year, and costs of 
pest control add an additional burden (Table 1). (The data in the table, which 
were accumulated from the U. S. Department of Agriculture, 3 do not include 
losses to livestock.) 

The data in Table 1 show that during the period from 1951 to 1960 the 
average cost of pesticides and application for insect control amounted to nearly 
$750 million per year. Because of resistance problems and an increasing number 
of pests, there is every reason to believe that this figure has increased markedly 
since 1960. Likewise, many herbicides were still in the development stage during 
1951 to 1960, and therefore at present herbicides make up much more than 8% 
of the total of the controls. With the exception of weed control (cultivation, 
disking, and plowing are still the major means of combatting weeds), agricultural 
chemicals carry the main burden of crop protection against potentially 
devastating losses. I calculated agrochemicals to be about 34% of the annual 
control costs during the period from 1951 to 1960. At the same time, the use of 
these chemicals adds greatly to disruptions in the agroecosystem. 



436 



STERN 



Table 1 

SUMMARY OF ESTIMATED AVERAGE ANNUAL LOSSES TO AGRICULTURAL 

COMMODITIES FROM VARIOUS HAZARDS AND COST OF CONTROLLING 

THESE LOSSES AND OF INSPECTION AND QUARANTINE PROGRAMS 

(1951-1960)* 



Kind of loss and control program 



Thousands of dollars 



Loss in 
value 



Cost of 
control 



Type of 
control, °/ 



Loss of Crops, Pasture, and Range Plants 



During production 
Diseases of crops and 

pasture and range plants 
Nematode damage 
Injurious insects 

Weeds in crops, pasture, 
and range land 

After production 

During storage (due to insect 
and other losses) 



3,251,114 


115,800 


Chemicals, 94 
Disease-free plants, 6 


372,335 


16,000 


Nematocides, 100 


3,812,406 


425,OOOt 


Insecticides, 99 
Cultural and biological, 1 


2,459,630 


2,551,050 


Cultural, 92 
Herbicides, 8 


1,042,063 


279,302 


Primarily insecticides 



Control Programs 



Cooperative plant-pest 
control programs 

Plant quarantine and 
regulatory programs 



Total 



24,521 



4,162 



10,937,548 



3,415,835 



Chemicals and other 
control measures 

Chemicals and other 
control measures 

Chemicals, 34 



*The estimates indicate not only preventable reductions in production but also, in some cases, 
losses not avoidable with present technical knowledge. For various reasons these must be 
interpreted as losses to the public rather than to farmers. (See USDA Agricultural Handbook 
No. 291, Ref. 3.) 

tFigures include cost of controlling insects affecting crops, man, animals, and households. 



AGROECOSYSTEMS AND NATURAL COMMUNITIES 



Agroecosystems as well as natural communities are usually considered to be 
self-sufficient habitats where the living organisms and the nonliving environment 
interact in the exchange of matter and energy in a continuing cycle. ' The 
natural community can exist without man, but the agroecosystem is manipu- 
lated by him and represents his efforts to control nature and to meet his need 
for food and other products. The degree of man's dominance in agroecosystems 
varies considerably from one area to another. Moreover, the causes of 
agroecological-induced arthropod disturbances are multitudinal and can often be 
correlated with the degree of man's activity in the systems. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 437 

An example of a simple agroecosystem with very little manipulation by man 
can be found on the rocky slopes and along the stream beds on the southwest 
coast of Turkey. This simple system extends from Izmir 200 to 300 miles south 
toward Antalya. For centuries a small number of people have lived in this area, 
surviving along the stream beds on small patches of grain and some vegetables, a 
few fish from the Aegean Sea, and some sheep and goat products. 

Recently the Food and Agriculture Organization of the United Nations 
supported the planting of thousands of olive trees on the nonproductive 
brush-covered slopes in 40-to-50-ft spaced natural contours to avoid erosion. In 
addition to his previous meager food sources, the Turkish peasant now has an 
olive crop, of sorts, but he does little more to the environment than keep the 
brush from closing in on the contoured olive-tree plantings. 

The original arthropod fauna in this area has changed slightly in response to 
the increased olive crop. There is now a higher number of olive fruit flies, Dacus 
oleae (Gmelin); olive moths, Prays oleae; oleander scales, Aspidiotus hederae 
(Vallot); and black scales, Saissetia oleae (Bernard). But these changes have been 
minor. 

At tne otner extreme is the once barren Imperial Valley in soutnern 
California, carved out of an ancient seabed and made into one of the most highly 
productive agroecosystems on earth. This valley receives about 1 to 3 in. of 
rainfall per year and is entirely dependent on irrigation water from the Colorado 
River 50 to 60 miles away. Agricultural production consists of a wide variety of 
fall, winter, and spring vegetables, citrus fruits, forage crops, vegetable seed 
crops, sugar beets, cotton, small grains, melons, beef cattle, etc. Only a minute 
fraction of the raw or processed products is consumed or used by the small 
number of inhabitants of the valley. 

Throughout the year irrigation water, fertilizers, insecticides, herbicides, 
fungicides, and nematocides are added to the environment as various fields are 
plowed, special crops are planted and harvested, and the plant debris is plowed 
under in preparation for the next crop. With the exception of high solar energy 
input nearly 365 days per year and the parent soil, this agroecosystem is entirely 
artificial and totally dependent on manipulation by man for its existence. 

Sixty years ago this valley was essentially uninhabited by man. There were a 
few insects present which were pests elsewhere, but they were of no concern in 
this valley since they did not compete with man for existence. Because of the 
present abundance of food and the very high temperatures in summer and 
moderate temperatures in winter, this valley is a perfect insectary. It now 
supports a large number of insect- and mite-pest species; in addition to the 
original potential pests, a large number of others have come from outside 
sources. Owing to a high input of pesticides with wide toxicity spectrum and to 
the continuous planting and plowing of short-lived annual crops, pest popula- 
tions are often present in damaging or potentially damaging abundance 
throughout the year in contrast to arthropods in natural communities. 



438 STERN 

Although the Imperial Valley is superficially different from agroecosystems 
in the midwestern, southern, and eastern United States, the causes of imbalance 
and eruption of pest species are similar in all agroecosystems. From one extreme 
to the other, the different types and structures of agroecosystems represent a 
type of stability because of the general continuity of man's special food plants 
grown under the prevailing climate as well as varying degrees of disturbance. 

By contrast, in natural communities where a wide variety of plant and 
animal species are meshed in complex food chains, it is uncommon that plants 
are massively destroyed by phytophagous insects. There are of course special 
cases where destruction occurs periodically, for example, the attacks on balsam 
fir in eastern Canada 6 bv the spruce budworm, Choristoneura fumiferana 
(Clemens); the attacks on lodgepole pine in California and elsewhere 7 by the 
lodgepole needle miner, Coleotechnites milleri (Busck); and the historical cases 
of plagues of grasshoppers and locusts in parts of Africa and Asia. 8 

The reasons for more-balanced population regulation in natural communities 
are generally believed to be the high degree of diversity, continuity, and stability 
in natural plant— animal communities as compared with simplified agroeco- 
systems. 9 ' 10 However, it is still debatable how these three factors interact to 
hold populations in check so that a single or a few species rarely cause disruption 
in these evolutionary-oriented ecological systems. In other words, in natural 
communities a verv strict police state exists and appears to be regulated by the 
organisms themselves to preserve an orderly population abundance system. 

In the evolution of all species at various trophic levels and in the complex 
interrelations of eating and being eaten, varying degrees of governing mecha- 
nisms have evolved to hold species populations in check.* Governing mecha- 
nisms that help to determine population levels within the framework or the 
potential set by other environmental elements include not only immediate or 
direct factors producing premature mortality, retarded development, or reduced 
fecundity 1 l but also all aspects of the environment. 

In contrast to this orderly system, in the agroecosystem man operates and 
controls the plant life and is often the main disrupting force. 



MAN AND HIS ARTHROPOD COMPETITORS 

In the past several centuries, man has developed a technology that permits 
him to greatly modify environments to meet his need for food and space. 
Modifying the environment for the competition between man and other 
organisms would appear to favor man, as is attested by the decimation of vast 
vertebrate populations, as well as populations of other forms of life. 12 But when 
man eliminated many species as he changed the natural communities into 



*Some definitions and explanations of terms are given in the appendix (pages 451—452) 
to clarify certain parts of this paper. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 



439 



agroecosystems, a number of other species, particularly the arthropods, became 
his direct competitors. 1 3 Thus, when early man subsisted in undisturbed natural 
communities as a huntsman or foraged for food from uncultivated sources, he 
was rarely confronted with exploding insect populations, except for sporadic 
eruptions of plagues of grasshoppers and locusts. 

Today, by contrast, as man's population continues to increase and his 
food-production activities are intensified, he is now in direct competition with 
thousands of phytophagous arthropod species. 

The increase in population numbers of a particular species to pest status may 
be the result of a single factor or a combination of factors. 

First, by changing or manipulating the environment, we can create 
conditions that permit certain species to increase their population density. 15 
The rise of the Colorado potato beetle, Leptinotarsa decemlineata (Say), from 
an unimportant species to one of major importance occurred in this manner 
(Fig. 1). Before 1850 this beetle existed in very low numbers feeding on sand 
burr, Solatium rostratum Dunal, and other plants along the eastern slopes of the 
Rocky Mountains. When the American pioneers moved westward, they planted 



i — i — r 



General equilibrium position 
after widespread potato culture 




General equilibrium position prior 
to widespread potato culture 



J I L 



TIME 



1850 1860 1870 



Fig. 1 Change in general equilibrium position of the Colorado potato beetle, 
Leptinotarsa decemlineata, after development of widespread potato culture in 
the United States. (For a discussion of the significance of economic-injury 
levels and economic thresholds in relation to the general equilibrium position, 
see section on the severity of pests and the definitions in the appendix.) 



440 



STERN 



the potato widely as one of their main food sources. Widespread cultivation of 
the potato was a change in the environment which was favorable to the beetle, 
and this enabled it to quickly become an important pest. Not only the increase 
of a new food source but also the plowing of the prairie and the destruction of 
forested regions aided in the expansion of its range of distribution. In a few 
years it was a pest in all of eastern North America. This beetle was unknowinglv 
transported to Europe after World War I and is now a major pest in that region 
also. 

Similarly, when alfalfa, Medicago sativa L., was introduced into California 
about 1850, the alfalfa butterfly, Co lias eury theme Boisduval, which had 
previously occurred in low numbers on native legumes, found a widespread and 
favorable new host plant in its environment and subsequently became an 
economic pest. 1 6 

A second way in which arthropods have risen to pest status is by being 
transported across geographical barriers and leaving behind their specific 
predators, parasites, and diseases. 17 For example, the cottony-cushion scale, 
leery a purchasi Maskell (Fig. 2), was introduced into California from Australia 
on ornamental acacia plants in 1868. Within two decades it increased in 
abundance to the point where it threatened economic disaster to the entire 



1 1 1 

^ — Introduction of 
/"\ Cryptochaetum iceryae 
/ \ and Rodolia cardinal is 




Resurgence produced by 

DDT in San Joaquin Valley— s^^ 




Economic-injury level 1 1 


J \ Economic threshold / \ 


I General \ 
/ equilibrium * 




/ i i i 



1868 



1888-1889 1892 



1947 



TIME 



Fig. 2 Fluctuations in population density of the cottony-cushion scale, Icerya 
purchasi, on citrus from the time of its introduction into California in 1868. 
After the successful introduction of two of its natural enemies in 1888, this 
scale was reduced to noneconomic status except for a local resurgence 
produced by DDT treatments about 1947. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 441 

citrus industry in California. Fortunately the timely importation and establish- 
ment of two of its natural enemies [the vedalia, Rodolia cardinalis (Mulsant) and 
Cryptochaetum iceryae (Williston)] from Australia resulted in the complete 
suppression of /. purchasi as a citrus pest. 1 The cottony-cushion scale again 
rose to major pest status in 1947 when the widespread use of DDT eliminated 
the vedalia on citrus in the San Joaquin Valley. 1 

A third cause for the increasing number of pest arthropods has been the 
establishment of progressively lower economic thresholds. This can be illustrated 
by lygus bugs, Lygus species, on lima beans. Not many years ago the blotches 
caused by lygus bugs feeding on an occasional lima bean were of little concern, 
and the bugs were considered a minor pest on this crop. With the emphasis on 
product appearance in the frozen-food industry, however, a demand was created 
for a near-perfect bean. For this reason very low economic-injury thresholds 
were established, and lygus bugs are now considered serious pests on lima beans. 

In addition to food-product appearance, which is often related to competi- 
tive marketing, certain marketing standards dictate a minimum degree of damage 
or insect parts permissible in or on raw or processed products. 20 At present 
these standards often impose severe requirements for chemical pest control. In a 
situation of critical food shortage following nuclear disaster, insects that affect 
commodity appearance or the presence of a few insect parts in or on food would 
undoubtedly be ignored. This in turn would help to alleviate any shortage of 
insecticides, and the chemicals available could be used in situations where entire 
crops are threatened. 

A fourth way by which insects can rise to pest status is by the elimination of 
biological control agents that hold a potential pest in check. 2 l Recent examples 
include the outbreak of the beet army worm, Spodoptera exigua (Hubner); the 
cabbage looper, Trichoplusia ni (Hubner); and bollworm, Heliothis zea (Boddie), 
following treatments with Azodrin, Bidrin, and other chemicals to control lygus 
bugs in cotton fields in the San Joaquin Valley.* The outbreak of the cotton leaf 
perforator, Bucculatrix thurberiella Busck, the beet army worm, and the cabbage 
looper following widespread chemical treatments for control of the pink 
bollworm, Pectinophora gossypiella (Saunders), in the Imperial Valley are others 
among many examples. 

The increased pest severity due to elimination of beneficial species by 
pesticides is of special interest in relation to radioactive fallout. At present, other 
than studies of radiation effects on honeybees and a few insect predators and 
parasites, there are few or no data to indicate whether radiation might act 
differentially on the entomophagous species (i.e., those feeding on other 
arthropods) in comparison with the phytophagous species. More research is 
needed in this area, particularly in the insect orders Hemiptera (sucking bugs), 
Coleoptera (beetles), Hymenoptera (bees, ants, and wasps), and Diptera (flies 



*R. van den Bosch, University of California, unpublished data. 



442 STERN 

and mosquitoes), which contain large numbers of beneficial species in addition 
to pest species. As matters now stand, nearly all the research on effects of 
radiation on arthropods has been conducted on pest species in relation to the 
male-sterilization technique for pest control. 



SEVERITY OF VARIOUS PEST SPECIES 

To determine the relative economic importance of pest species, we must 
consider both the economic threshold and the general equilibrium position of 
the pest. The general equilibrium position and its relation to the economic 
threshold, in conjunction with the frequency and amplitude of fluctuations 
about the general equilibrium position, determine the severity of a particular 
pest problem. 

In the absence of permanent modification in the environment, the density of 
a species tends to fluctuate about the general equilibrium position as changes 
occur in the biotic and physical components of the environment. As the 
population density increases, the density-governing factors respond with greater 
and greater intensity to check the increase; as the population density decreases, 
these factors relax in their effects. The general equilibrium position is thus 
determined by the interaction of the species population, the density -governing 
factors, and the other natural factors of the environment. A permanent 
alteration of any factor of the environment, either physical or biotic, or the 
introduction of new factors may alter the general equilibrium position. 1 3 

The economic threshold of a pest species can be at the level of or at any level 
above or below the general equilibrium position. Some phytophagous species 
utilize our crops as a food source but even at their highest attainable density are 
of little or no significance to man (Fig. 3). Such species can be found associated 
with nearly every crop of commercial concern. 

Another group of arthropods rarely exceeds the economic threshold and 
consequently are occasional pests. Onlv at their highest population density will 
chemical control be necessary (Fig. 4). 

When the general equilibrium position is close to the economic threshold, 
the population density will frequently reach this threshold (Fig. 5). In some 
cases the general equilibrium position and the economic threshold are at 
essentially the same level. Thus insecticidal treatment is necessary each time the 
population fluctuates up to the level of the general equilibrium position. In such 
species the frequency of chemical treatments is determined by the fluctuation 
rate about the general equilibrium position, which in some cases necessitates 
almost continuous treatment. 1 3 

Finally, for some pest species the economic threshold lies below the general 
equilibrium position. These constitute the most severe pest problems in 
entomology (Fig. 6). The economic threshold may be lower than the level of the 
lowest population depression caused by the physical and biotic factors of the 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 



443 




TIME 



Fig. 3 Noneconomic population whose general equilibrium position and 
highest fluctuations are below the economic threshold, e.g., Aphis medicaginis 
Koch on alfalfa in California. 




TIME 



Fig. 4 Occasional pest whose general equilibrium position is below the 
economic threshold but whose highest population fluctuations exceed the 
economic threshold, e.g., Grapholitha molesta Busck on peaches in California. 



444 



STERN 




TIME 



Fig. 5 Perennial pest whose general equilibrium position is below the 
economic threshold but whose population fluctuations frequently exceed the 
economic threshold, e.g., Lygus species on alfalfa seed in the western United 
States. 




TIME 



Fig. 6 Severe pest whose general equilibrium position is above the economic 
threshold and for which frequent and often widespread use of insecticides is 
required to prevent economic damage, e.g., Musca domestica in Grade A 
milking sheds. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 



445 



environment, e.g., many insect vectors of viruses. In such cases, particularly 
where human health is concerned, there is a widespread and almost constant 
need for chemical control. This produces conditions favorable for development 
of insecticide resistance and other problems associated with heavy treatments. 

DISPERSION OF PEST SPECIES 

A species population is flexible and undergoes constant change within the 
limits imposed upon it by its genetic constitution and the characteristics of its 
environment. Typical fluctuations in population density and dispersion are 
shown in Fig. 7. The population dispersions shown at the three points in time, 



<^SH> A 








1 

A 


<*&£$£& 


A- 

/ \General equilibrium position\ 


w 






J" W ""n 


1/ ^ 





TIME 



Fig. 7 Population trend and population dispersion of a pest species over a 
long period of time. — , fluctuations in the population density with time;—, 
general equilibrium position. A, B, and C, population dispersion at specific 
times. The basal area of models A, B, and C reflects the distributional range, 
and the height indicates population density. Population densities above the 
economic threshold are black. 



A, B, and C, are not static but rather are instantaneous phases of a continuously 
changing dispersion. 1 

Thus at point A, when the population is of greatest numerical abundance, it 
also has its widest distributional range (as depicted by the maximum diameter of 
the base of the model) and is of maximum economic status (as depicted by the 
number and magnitude of the blackened pinnacles representing penetrations of 



446 STERN 

the economic threshold). At point B, on the other hand, when the species 
population is at its lowest numerical abundance, it is generally most restricted in 
geographical range and is of only minor economic status. Point C represents an 
intermediate condition between points A and B. 

Figure 8, which is related to Fig. 7, illustrates the relation between the 
geographic distribution of a species and the interrelatedness of physical and 



ABSOLUTE 
LIMIT 




Zone 1 Stable zone of permanent occupancy; most nearly optimal physical conditions. 
Zone 2 Intermediate zone of permanent occupancy; physical conditions intermediate. 
Zone 3 Marginal zone of permanent occupancy; physical conditions rigorous, mostly 

unfavorable; at very limited places permanently permissive. 
Zone 4 Zone of only temporary occupancy; physical conditions only temporarily 

permissive anywhere; dependent on immigration. 

Fig. 8 Geographic distribution of a species population and the interrelation 
of conditioning and regulating forces. Physical factors are never permissive for 
occupancy beyond zone 4. (Data from C. B. Huffaker and P. Messenger, The 
Concept and Significance of Natural Control, in Biological Control of Insect 
Pests and Weeds, P. DeBach (Ed.), Chap. 4, Reinhold Publishing Company, 
New York, 1964.) 

biotic factors in the environment. Each circle (zone) of the concentric series 
represents a type of environment. The irregular patches in each zone represent 
localized areas of relative permanent favorability in regard to physical 
conditions, and the interspaces represent the degree of waxing and waning of 
such areas in time. 

The relative sizes of these zones as shown here have no significance. One 
species, such as the corn earworm, H. zea, may range over thousands of square 
miles; another species may be restricted to one or two states or even less. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 447 

The environment of zone 1 has nearly optimal climatic conditions, at least 
during a certain part of the year, and permits an increase in numbers generation 
after generation. In the environment of zone 4, at the other extreme, only 
temporary existence is possible. If any part of the species population is 
eliminated in part of its range by pesticides, radioactive fallout, use of sterile 
males, unfavorable heat or cold, elimination of food, etc., the survivors in the 
adjoining areas will repopulate the disturbed area once the unfavorable factor 
has disappeared. The rate of reinvasion will depend on prevailing physical factors 
and on the flight habits, behavior, and ecology of the species involved. 

In the environment of zone 1, essentially the total area is represented by 
maximum favorability in the physical framework of the environment; hence 
there is little room for changing physical conditions to alter population 
potential. 

In the environment of zone 3, on the other hand, permanently favorable 
localized habitats are greatly reduced. Thus the waxing and waning of 
population potentials is a dominant feature relative to climatic factors causing 
population change. However, the role of physical forces and natural enemies is 
still the same as in the environments of zones 1 and 2. In the environment of 
zone 4, migrants from the more favorable areas are necessary to populate the 
area when favorability is temporarily permitted. 

THE MONOCULTURE AND ITS INHERENT ARTHROPOD PROBLEMS 

Earlier in this discussion arthropod populations in a very simple agroeco- 
system with little interference from man (the southwest coast of Turkey) and in 
a highly intensified system with great interference from man (the Imperial 
Valley) were contrasted to arthropod populations in natural communities. 
Another type of agroecosystem that is quite similar to the Imperial Valley but 
differs in plant and animal composition is the monoculture developed in parts of 
the Midwest and in sections of the western United States. In these systems the 
tendency of pest populations to appear in damaging numbers year after year is 
almost an accepted fact. 

A good example of a monoculture occurs on the west side of the San 
Joaquin Valley. This particular portion of the valley is 30 to 40 miles wide and 
about 150 miles long. Farming operations are very large in comparison with 
other parts of the United States. The individually owned and corporate farms 
range from very small operations of 3 to 4 square miles of irrigated farm land 
upward to nearly 175 square miles of highly intensified irrigated agriculture. 

The only trees and shrubs in this area are those planted around a few widely 
scattered ranch headquarters. The commercial plants, literally the only plants 
permitted to grow in this area, are pure stands of cotton, safflower, cantalopes, 
alfalfa as a seed crop, barley, tomatoes, and sugar beets. Rarely is a crop planted 
in a field smaller than 160 acres. All other plants are destroyed by a preplant 



448 STERN 

herbicide or by cultivation. Weeds germinating along the edges of fields and 
roads after the winter rains are disked under in early spring after the rains cease, 
or they are destroyed by desiccating oils. 

Increasing to damaging numbers each year are tremendous populations of 
lygus bugs, Lygus besperus Knight and L. elisus Van Duzee; cabbage loopers, T. 
ni; beet army worms, S. exigua; bollworms, H. zea; spider mites, Tetranychus 
species; spotted alfalfa aphid, Therioaphis tnfolii (Monell); and other insects. 

Lygus bugs increase to high numbers in the winter safflower crop and in the 
alfalfa seed crop. 24 When the safflower begins to dry in late spring, the lygus 
bugs fly to cotton, and chemical treatments begin. Nearly all the lepidopterous 
pests increase to high numbers following the early chemical treatments for lygus 
bugs, which destroy the predators and parasites of these pests.* These worm 
species come from outside sources, survive because of resistance to the chemical, 
or are protected in the soil and elsewhere at the time of treatment. With the 
elimination of their predators and parasites, these pests are free to increase 
unhindered. 

Treatments with some chemicals, such as Azodrin or Bidrin, are more drastic 
in their ecological effects than treatments with Dylox. In fact, the disruptive 
effects of Azodrin on birdlife and the resurgence of secondary insect-pest 
species following treatment are very noticeable; thus this chemical cannot be used 
in California after July 15 each year. Theoretically this should permit a time 
interval for the predators and parasites to reenter the treated fields and become 
reestablished. However, our preliminary data indicate that, once the arthropod 
food chain is destroyed, the insect usually does not become reestablished for the 
remainder of the season. 

If pest control could be considered as a single factor, work toward the 
development of complex polycultures as opposed to the monoculture type of 
agriculture would be highly desirable. The interplanting of various species and 
varieties of crops in complex polycultures may result in yields of total biomass 
equal to or greater than those produced in monocultures. However, pest control 
is only one aspect of food production. It remains to be seen whether American 
farming systems can be devised which are of satisfactory efficiency in carrying 
out all the agronomic practices in such a complex mixture of crops. Converting 
monocultural systems back to mixed agriculture demands further economic 
study since much of the success of the American farmer stems from research and 
development leading to simplifying the agroecosystem. Likewise, the physical 
factors of soil and climate often predetermine special types of crops most 
economically productive for a given area. Furthermore, the era of the 
family-type diversified farm is past, and farmers on a regional basis find it most 
profitable to concentrate on a few specialized crops best suited for that area. 



*V. M. Stern and R. van den Bosch, University of California, Riverside, unpublished 
data. 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 449 

This is quite noticeable when we survey the acreages of rice, corn, potatoes, 
vegetables, peas, beans, sugar beets, sugarcane, soybeans, vineyards, and 
orchards as they are distributed in the United States. 25 

SIMILARITY OF PESTICIDES AND FALLOUT RADIATION 

With the exception of field tests of relatively small size and laboratory 
radiation studies on 100 to 200 insect and mite species selected from the 2 
million arthropod species, there is little information concerning the effects that 
fallout may have on arthropod populations over wide areas. 22 However, some 
comparisons might be made between the ecologically disruptive effects of the 
use of widely toxic pesticides and radioactive fallout. This comparison requires 
some information concerning the development and nature of commercial 
pesticides. 

One reason for ecological disruption arising from modern pesticides stems 
from the manner in which these compounds are developed commercially. During 
development and in registering, essentially no ecological considerations enter 
into the search for new compounds. The candidate materials are screened on the 
basis of maximum kill on 8 to 12 laboratory cultures of pest species and for 
phytotoxicity. The basic considerations as to whether a particular compound 
will be developed are: (1) the size of the potential market for the compound, 
(2) competing products in that market and the company's patent control over 
the new product and its competitors, (3) the possibilities of recouping 
development costs and returning a profit, and (4) certain safety factors with 
respect to residues, application, and human health. 

Under this system the ideal material from the commercial viewpoint is one 
that can be registered and labeled for use against a very broad spectrum of pests 
on a wide variety of crops. 

It is precisely this type of compound with a broad toxicity spectrum which 
kills not only pest species but also beneficial insects (plant pollinators, predators, 
and parasites). As a result, a large proportion of these compounds are 
ecologically disruptive. 4 ,5 ' l 3 

When pesticides are used for control, they involve only immediate and 
temporary reduction of populations and do not contribute to permanent 
pest-density regulation. Theoretically they are employed to reduce pest species 
that rise to dangerous levels when natural enemies of the pest and other 
environmental pressures are inadequate. 

On some occasions the pest outbreak and the application of a pesticide for 
its control may cover a wide area, e.g., the outbreak of the spruce budworm, C. 
fumiferana, in northeastern Canada 6 or of lygus bugs, L. hesperus and L. elisus, 
in the San Joaquin Valley. 24 In other instances damaging numbers of pests may 
occur in restricted locations. In either case these outbreaks occur during the 
season favorable to the pest, with the relaxed environmental pressures occurring 



450 STERN 

sometime before the outbreak. As mentioned previously, in our agroecosystems 
we often simplify and change the environment to such a degree that the 
environmental pressures holding pests in check are totally inadequate. 

Since most pest species have wide ranges of distribution (often hundreds of 
miles and from one state to another), the treated area is always subjected to 
reinvasion from individuals outside the area or by rapid resurgence from those 
not destroved within the treated area. 

In some ways, other than genetic changes induced by radiation and 
phototoxicity, radioactive fallout can be similar to insecticides. It is well known 
that some insecticides do exhibit differential killing effects on various species 
when applied at commercial dosages. Of course, 20 lb of actual Azodrin per acre 
will probably eliminate all the exposed arthropods, and probably the plants as 
well; so will radiation doses of 100 kR. However, LaChance 23 in discussing 
insect sterility data, points out that radiation also has differential effects on 
arthropods. Most Dipteran species can be sterilized with doses under 10 kR, but 
within this order a threefold difference was noted. The Hymenoptera require 
about 6 to 10 kR, and most Coleoptera seem to sterilize at 4 to 10 kR. On the 
other hand, the Lepidoptera, essentially all species of which are phytophagous 
and which includes some of the most ravaging species on earth, requires very 
large doses to produce sterility. Thus radiation can be similar to insecticides as 
far as its differential effects on insects are concerned. In both cases the reasons 
for these differential effects is not entirely clear. In regard to radiation, more 
research on interphase nuclear volumes or nuclear DNA content may be required 
before comparisons are meaningful. 

The data of Miller and Callahan et al. indicate that after a nuclear 
disaster there will be areas with sufficiently low radiation fields to permit 
survival of manv pest arthropods because as a group these insects are quite 
tolerant to radiation and most pest species have wide ranges of distribution. The 
pest species can be expected to reinvade the disturbed area as soon as the effects 
of radiation are low enough for plants to become established. The mobility of 
insect-pest species attacking our major food crops and their reinvasion time after 
elimination from wide areas were reported previously. 

For the reasons mentioned, radioactive fallout would appear to act similarly 
to an insecticide in its disruptive effects on arthropods. Pesticides are usually 
added to a restricted segment of the environment to eliminate a localized 
population. Because insecticides and radioactive fallout are nonreproductive, 
have no searching capacity, and are more or less nonpersistent (as far as 
continuous killing effects are concerned), they constitute short-term, restricted 
pressures. These types of materials cannot permanently change the general 
equilibrium position of the pest population, nor can they restrain an increase in 
abundance of the pest without repeated applications. Therefore to destroy pests 
they must be added to the environment at varying intervals of time. 

After a chemical application the pest population density may be far below 
the economic threshold and below its general equilibrium position, but, since the 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 451 

insecticide is not a permanent part of the environment, the pest usually returns 
to a high level when the effects of the insecticide are gone. 

These killing measures have little influence on the pest in adjoining areas 
except as localized population depressants. 

In the highest-radiation field, certain insect species would undoubtedly be 
nearly completely eliminated. Away from the high-radiation field, there would 
be less mortality and various types of genetic change. Whether the offspring of 
these individuals could survive and compete in nature is unknown. 

However, individuals from low-radiation areas would be invading the 
disturbed area even before the radiation had disappeared. By continuous 
reinvasion individuals would eventually become established as soon as plant 
species were available for food. For these and the reasons mentioned earlier, pest 
insects and their control can be expected to be important considerations in food 
production in the event of nuclear disaster. 

APPENDIX: DEFINITION OF TEFIMS 

Biological control. The action of parasites, predators, or pathogens on a host or 
prey population which produces a lower general equilibrium position than would 
prevail in the absence of these agents. Biological control is a part of natural 
control, and in many cases it may be the key mechanism governing the 
population levels within the framework set by the environment. If the host or 
prey population is a pest species, biological control may or may not result in 
economic control. 

Economic control. The reduction or maintenance of a pest density below the 
economic-injury level. 

Economic-injury level. The lowest population density that will cause economic 
damage. Economic damage is the amount of injury which will justify the cost of 
artificial control measures; consequently the economic-injury level may vary 
from area to area, from season to season, or with man's changing scale of 
economic values. 

Economic threshold. The density at which control measures should be 
determined to prevent an increasing pest population from reaching the 
economic-injury level. The economic threshold is lower than the economic- 
injury level to permit sufficient time for initiation of control measures and for 
these measures to take effect before the economic-injury level is reached. 

General equilibrium position. The average density of a population over a period 
of time (usually lengthy) in the absence of permanent environmental change. 
The size of the area involved and the length of the period of time will vary with 
the species under consideration. Temporary artificial modifications of the 
environment may produce a temporary alteration of the general equilibrium 
position (i.e., a temporary equilibrium). 



452 STERN 

Governing mechanism. The actions of environmental factors, collectively or 
singly, which intensify as the population density increases and relax as this 
density falls so that population increase beyond a characteristic high level is 
prevented and decrease to extinction is made unlikely. The governing mecha- 
nisms operate within the framework or potential set by the other environmental 
elements. 

Natural control. The maintenance of a more or less fluctuating population 
density within certain definable upper and lower limits over a period of time by 
the combined actions of abiotic and biotic elements of the environment. Natural 
control involves all aspects of the environment, not just those immediate or 
direct factors producing premature mortality, retarded development, or reduced 
fecundity but remote or indirect factors as well. For most situations, governing 
mechanisms are present and determine the population levels within the 
framework or potential set by the other environmental elements. Natural control 
of a pest population may or may not be sufficient to provide economic control. 

Population. A group of individuals of the same species that occupies a given 
area. A population must have at least a minimum size and occupy an area 
containing all its ecological requisites to display fully such characteristics as 
growth, dispersion, fluctuation, turnover, dispersal, genetic variability, and 
continuity in time. The minimum population and the requisites in an occupied 
area will vary from species to species. 

Population dispersion. The pattern of spacing shown by members of a 
population within an occupied habitat and the total area over which the given 
population may be spread. 

Temporary equilibrium position. The average density of a population over a 
large area temporarily modified by a procedure such as continued use of 
insecticides. The modified average density of the population will revert to the 
previous or normal density level when the modifying agent is removed or 
expended. (Cf. General equilibrium position.) 

REFERENCES 

1. R. D. O'Brien and L. S. Wolfe, Radiation, Radioactivity, and Insects, Academic Press, 
Inc., New York, 1964. 

2. P. DeBach (Ed.), Biological Control of Insect Pests and Weeds, Reinhold Publishing 
Corporation, New York, 1964. 

3. U. S. Department of Agriculture, Losses in Agriculture, Agriculture Handbook No. 291, 
Superintendent of Documents, U. S. Government Printing Office, Washington, D. C, 
August 1965. 

4. R. F. Smith and R. van den Bosch, Integrated Control, in Pest Control, W. W. Kilgore 
and R. L. Doutt (Eds.), Chap. 9, Academic Press, Inc., New York, 1967. 

5. R. van den Bosch and V. M. Stern, The Integration of Chemical and Biological Control 
of Arthropod Pests, Ann. Rev. Entomol, 7: 367-386(1962). 



INSECT-INDUCED AGROECOLOGICAL IMBALANCES 453 

6. R. F. Morris (Ed.), The Dynamics of Epidemic Spruce Budworm Populations, Mem. 
Entomol. Soc. Can., No. 31, 1963. 

7. A. D. Telford, Features of the Lodgepole Needle Miner Parasite Complex in California, 
Can. Entomol., 93(5): 394-402 (1961). 

8. O. B. Lean, FAO's Contribution to the Evaluation of International Control of the Desert 
Locust, 1951 — 1963, Food and Agriculture Organization of the United Nations, Rome, 
1965. 

9. C. B. Huffaker, Summary of a Pest Management Conference — a Critique, in 
Concepts of Pest Management, R. L. Rabb and F. E. Guthrie (Eds.), pp. 227-242, 
University of North Carolina Press, Chapel Hill, 1970. 

10. R. L. Doutt, Biological Control, in Pest Control, W. W. Kilgore and R. L. Doutt (Eds.), 
Chap. 1, Academic Press, Inc., New York, 1967. 

11. C. B. Huffaker and P. Messenger, The Concept and Significance of Natural Control, in 
Biological Control of Insect Pests and Weeds, P. DeBach (Ed.), Chap. 4, Reinhold 
Publishing Company, New York, 1964. 

12. W. L. Thomas, Jr. (Ed.), Man's Role in Changing the Face of the Earth, The University 
of Chicago Press, Chicago, 1956. 

13. V. M. Stern, R. F. Smith, R. van den Bosch, and K. S. Hagen, The Integration of 
Chemical and Biological Control of the Spotted Alfalfa Aphid. The Integrated Control 
Concept, Hilgardia, 29(2): 81-101 (1959). 

14. C. W. Sabrasky, How Many Insects Are There? Insects, Yearbook of Agriculture, 
pp. 1—7, U. S. Department of Agriculture, Washington, D. C, 1952. 

15. G. C. Ullyett, Mortality Factors in Populations of Plutella maculipennis (Tineidae: Lep.) 
and Their Relation to the Problem of Control, South African Dept. Agr. and Forestry 
Ent. Mem., 2(6): 77-202 (1947). 

16. R. F. Smith and W. W. Allen, Insect Control and the Balance of Nature, Sci. Amer., 
190(6): 38-42 (1954). 

17. R. F. Smith, The Spread of the Spotted Alfalfa Aphid, Therioaphis maculata (Buchton), 
in California, Hilgardia, 28(21): 647-691 (1959). 

18. R. L. Doutt, Vice, Virtue and the Vedalia, Ent. Soc. Amer., Bull, 4(4): 119-123 
(1958). 

19. W. H. Ewart and P. DeBach, DDT for Control of Citrus Thrips and Citricola Scale, Calif. 
Citrograph, 32: 242-245 (1947). 

20. California State Department of Agriculture, Agriculture Code, Standardization Pro- 
visions of Administrative Code and Standardization Procedures, Sacramento, 1964. 

21. R. van den Bosch and V. M. Stern, The Integration of Chemical and Biological Control 
of Arthropod Pests, A nn. Rev. Entomol., 7: 367-386 (1962). 

22. V. M. Stern, Insect Pests of Major Food Crops, Their Reinvasion Potential and the 
Effects of Radiation on Arthropods, OCD Work Unit No. 3145B, University of 
California, 1969. 

23. L. E. LaChance, C. H. Schmidt, and R. C. Bushland, Radiation-Induced Sterilization, in 
Pest Control, W. W. Kilgore and R. L. Doutt (Eds.), Chap. 4, Academic Press, Inc., New 
York, 1967. 

24. V. M. Stern et al., Lygus Control by Strip Cutting Alfalfa, Report AXT-241, University 
of California, Agricultural Extension Service, 1967. 

25. U. S. Department of Commerce, Bureau of the Census for the 1959 Census of 
Agriculture, Superintendent of Documents, U. S. Government Printing Office, Washing- 
ton, D.C., 1965. 

26. C. F. Miller, Fallout and Radiological Countermeasures. Vols. 1 and 2, SRI Project 
No. 1M-4021, Stanford Research Institute, 1963. 

27. E. D. Callahan et al., The Probable Fallout Threat Over the Continental United States, 
Report No. TO-B60-13, Technical Operations Inc., 1960. 



ECOLOGICAL EFFECTS OF ACUTE 
BETA IRRADIATION FROM SIMULATED 
FALLOUT PARTICLES 
ON A NATURAL PLANT COMMUNITY 



PETER G. MURPHY* and J. FRANK McCORMICK 

Department of Botany, University of North Carolina, Chapel Hill, North Carolina 



ABSTRACT 

9 
Simulated-fallout particles overcoated with Y were applied at two levels of activity to 

granite-outcrop plant communities. The experiment resembled conditions expected at a site 

170 miles downwind of a 2.5-Mt detonation with a wind velocity of 15mph. Mean 

community dose levels were 7000 and 4000 rads. In the 7000-rad communities, the ratio of 

mean ground-surface dose (8770 rads) to mean canopy dose (5092 rads) was 1.7. In the 

4000-rad communities, the mean ground-surface dose (4824 rads) was 1.6 times higher than 

the mean canopy dose (2996 rads). 

In the 7000-rad communities, the death of 46% of all terminal buds in the dominant 
Viguiera porteri resulted in a 37% height-growth reduction, a compensatory lateral branch 
development, a 16% reduction in community biomass, and a lower, more clumped, vertical 
distribution of leaves in the canopy. Comparison with earlier studies indicated that acute 
beta irradiation may be twice as effective as chronic gamma irradiation at equivalent total 
doses in causing height-growth reduction in V. porteri. 

No radiation-induced change in the metabolism of the outcrop ecosystem was detected 
through measurements of CGs exchange 43 days after fallout dispersal. The mean rate of 
net production on clear days in both July and September (9:30 a.m. to 4:40 p.m.) was 
1.2 g C/m /hr. Early nighttime rates of respiration (9:30 to 10:10 p.m.) averaged 
2.9 g C/m"/hr in July and 2.2 g C/m /hr in September. 

Only since 1959 have the effects of ionizing radiation on entire plant 
communities and ecosystems been experimentally investigated. McCormick's 
study of a granite-outcrop plant community 1 and Woodwell's study of a Long 
Island forest 2 were among the first investigations of radiation effects in natural 
plant communities. A common finding of these and subsequent studies has been 
that ecosystems respond to radiation stress much as they do to other 



*Present address: Department of Botany and Plant Pathology, Michigan State 
University, East Lansing, Mich. 

454 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 455 

environmental stresses. An overall setback in successional status is a basic pattern 
observed. Ionizing radiation therefore becomes of interest as a tool for studying 
mechanisms of adjustment, or homeostasis, in ecosystems. 

Piatt 3 pointed out that ionizing radiation is an environmental stress on 
organisms and ecosystems and as such must be considered as another 
environmental factor. In an interesting discussion Odum 4 explained that many 
of the consequences of ionizing radiation in ecosystems are not unique and can 
result from a variety of nonnuclear forces in the biosphere. Woodwell 5 discussed 
ionizing radiation and fallout as model pollutants and in a subsequent article 6 
pointed out similarities between radiation effects and the effects of fire, oxides 
of sulfur, and herbicides. It is apparent that studies of the interaction of ionizing 
radiation with biological systems are of ecological interest not only for the 
information they supply on specific radiation effects but also for their 
contribution toward an understanding of the relation between structure and 
function in ecosystems. 

In studies of the effects of radiation on vegetation, the tendency has been to 
consider only gamma radiation of importance if the dose is from sources 
external to the vegetation and beta radiation of significance only as an internal 
factor. Until recently it was generally assumed that the limited penetrating 
ability of external beta radiation would prevent its causing serious damage to 
vegetation. Rhoads, Piatt, and Harvey, 7 however, reported that, in the Palanquin 
nuclear excavation experiment, sagebrush appeared much more sensitive to 
fallout than predictions based on experiments with gamma radiation from a 
60 Co source indicated that it should be. This finding led to the proposal that the 
sagebrush retained fallout particles relatively efficiently and that the beta 
component of the fallout radiation was important in producing the observed 
effects. It is now generally recognized that plant tissues near exposed plant 
surfaces are vulnerable to external beta radiation. 8 The dose received by such 
tissues as meristems may be large because of the high linear-energy-transfer 
coefficient of beta radiation. 

Within the last several years, a number of studies have been initiated using 
laboratory-produced radioactive particles as a fallout simulant; beta and gamma 
radiations were considered independently. Witherspoon and Taylor 9 l 1 studied 
the effects of external beta radiation, including the effect from simulated fallout 
particles, on higher plants and determined the doses necessary to produce 
various degrees of response. Apical meristems were killed by beta-bath doses of 
925 rads in white pine, 2315 rads in red oak, and 5400 rads in cocklebur when 
the doses were administered over a 1- to 3-day period. Other studies employed 
beta-emitting gauze strips applied to leaves 1 2 and cylinders placed over buds 9 to 
study external beta effects. Lane and Mackin, 12 who studied bean plants, were 
among the first to approach the issue of external beta radiation, and their data 
indicated that beta doses of 100,000 rads to leaves and 2000 rads to whole 
plants produced sterility. None of the relatively few reports concerning the gross 



456 MURPHY AND McCORMICK 

effects of external beta radiation on plants have dealt with entire plant 
communities. 

The primary objective of this study is to determine, qualitatively and 
quantitatively, the changes that occur in a natural plant community due to an 
acute exposure to external beta radiation from particles of a size range found in 
close-in fallout. Related objectives are (1) to describe the pattern of the 
radiation field produced by simulated fallout; (2) to obtain an index of the 
severity of beta effects relative to gamma effects observed in other studies, i.e., 
an ecological relative biological effectiveness factor (RBE); and (3) to describe 
some of the relations of structure and function in an ecosystem exposed to 
environmental stress. 



THE GRANITE-OUTCROP ECOSYSTEM 

Plants occur in small communities wherever soil accumulates in depressions 
on granite outcrops in the southeastern United States. The communities are 
found in small, often circular, depressions as well as in strips along the edges of 
forests adjacent to the rock. There are approximately 40 plant species that are 
considered characteristic of these communities although more than twice that 
many may occur in a community. 1 The species are zoned within the 
communities in response to intensity gradients of biotic and abiotic factors, soil 
depth and soil moisture being most important. The larger, deeper-rooted plants 
occur in the deeper soil, and in circular communities the zones are represented 
by concentric bands of the various species. 

The same attributes that favored the use of outcrop communities in the early 
work with gamma radiation 1 are also favorable attributes for analysis of 
beta-radiation effects. Their relatively simple composition and well-defined 
boundaries make them especially attractive for experimentation. An entire 
community can be studied as a microcosm, or small segments can be isolated and 
studied independently. Simulated rock outcrops can be constructed of concrete, 
as they have been at Emory University and the University of North Carolina, and 
the small ecosystems transplanted for more closely controlled investigation. 14 

There is an extensive literature dealing with various aspects of granite- 
outcrop ecosystems. Lugo 15 presented a survey of this literature along with 
energy, water, and carbon budgets for the system. The first published reports of 
an ecosystem experimentally irradiated in nature dealt with a granite-outcrop 
ecosystem, 1,16 18 and data from these early studies showed that gamma 
radiation from 60 Co had both stimulatory and inhibitory effects on plant 
growth. Species interactions at the community level reflected radiation effects 
on individual plants. 

The small size, relative simplicity, and adaptability for transplantation make 
these systems ideal experimental units. The considerable history of ecological 
research further enhances their suitability. For these several reasons the 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



457 



granite-outcrop ecosystem was selected for initial studies of the ecological 
effects of beta radiation from simulated fallout particles. 

METHODS 
Simulated Outcrops 

Five experimental communities were transplanted from Mt. Arabia, Ga., to 
two large concrete pads in the North Carolina Botanical Garden. Each pad had 
four circular depressions 2 m in diameter and 20 cm deep which had previously 
been coated with a thin layer of tar and covered with powdered granite as 
described by Cumming 1 9 to simulate the natural granite substrate. A sampling 
grid of 20- by 40-cm quadrats was established in each community. Four of the 
communities, in the process of being treated with fallout simulant, are shown in 
Fig. 1. 




Fig. 1 Simulated granite-outcrop communities in the process of being treated 
with fallout simulant. 



458 MURPHY AND McCORMICK 

Each circular community was divided through the center by a plexiglass 
sheet 1 cm thick and 1.2 m high. One-half of each of four communities was 
treated with radioactive fallout simulant, and the other half served as a control. 
(Each semicircle is referred to as a community.) A "low" dose of beta radiation 
was administered to two of the communities and a "high" dose to the other two. 
One-half of the fifth divided circular community was treated with nonradio- 
active fallout simulant as a control on physical particle effects. In studying 
radiation effects, we compared each irradiated community (semicircle) with the 
immediately adjacent control community on the opposite side of the plexiglass 
partition. 

The summer flora was selected for irradiation. Between June and October 
the annual herb Viguiera porteri (A. Gray) Blake, a member of the Asteraceae, 
dominates the outcrop community. Since the structure of the summer 
community is most dependent on this species. Viguiera was studied more 
intensively than the other species were. 

Irradiation and Dosimetry 

The fallout simulant, supplied by Stanford Research Institute (SRI), 
consisted of albite (sodium feldspar) particles 44 to 88 {J. in diameter with the 
beta-emitting isotope 9 Y overcoated on the particles with sodium silicate. 
Yttrium-90 has a 64.2-hr half-life and a beta energy of 2.26 MeV. The isotope 
solubility was 0.1 to 0.01%. These properties provided for an acute exposure to 
beta radiation from particles of a size range found in close-in fallout. 

The simulant was dispersed on July 31, 1969. Two communities were 
treated with simulant of 1.85 mCi/g activity, and the other two received 
simulant of 4.74 mCi/g. The density dispersed was the same in all applications, 
111 g per square meter of plant community (each community was 1.9 m 2 in 
area). The doses obtained from these applications were intended to be within a 
range capable of causing biological effects in outcrop plants, as previously shown 
in gamma-field studies. 18 Nonradioactive fallout simulant was applied to 
one-half of the fifth divided community (111 g/m 2 ). 

The experiment most closely resembled conditions expected at a site 
170 miles downwind of a 2.5-Mt detonation with a wind velocity of 15 mph 
according to calculations by Lane (personal communication) based on the 
procedures of Clark and Cobbin. 20 

A hand-held applicator consisting of two concentric plastic cylinders, the 
central cylinder containing the fallout simulant and the space between the two 
cylinders containing water for shielding, was used to disperse the simulant over 
the communities (Fig. 1). A sampling grid was used to help keep the distribution 
of particles uniform. After fallout dispersal the communities were covered with a 
light cheesecloth tent for 1 week to reduce wind velocity and fallout 
redistribution from the concrete pad to the surrounding area. A 1.5-cm rainfall 
24 hr after fallout dispersal washed all visible particles off exposed surfaces of 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 459 

the vegetation onto the soil surface. No radioactive particles were detected with 
a portable G— M counter off the concrete pad containing the experimental 
communities. 

Lithium fluoride thermoluminescent dosimeters (3 mm square and 1 mm 
thick), wrapped in light-shielding material and sealed in polyethylene packages, 
were placed in all treatment and control communities at two vertical levels 
(ground surface and 40 cm above the ground) on thin wooden rods. Forty-five 
dosimeters were placed in each treatment community and 12 in each control 
community. The 40-cm height represented the average height of terminal buds in 
the summer-dominant Viguiera porteri. When Landauer & Co. read the dosime- 
ters after a 3 3-day exposure, less than 0.1% of the initial radioactivity remained. 
Landauer's values were then multiplied by a correction factor of 1.18 
determined from exposure of six dosimeters to known dose levels of beta 
radiation from a calibrated 90 Y source 2 x by J. Mackin at SRI. 

Ten glass-vial dosimeters containing lithium fluoride were arranged vertically 
on a string, five in each of the high-dose communities. These dosimeters, which 
were collected after the first 27 hr of exposure by W. Lane of SRI, provided an 
estimate of initial dose rates and vertical stratification of doses before the fallout 
simulant was washed from the vegetation by rain. 

The percentage of retention of the fallout simulant was estimated by using 
nonradioactive simulant. Twenty planchets (total area, 151 cm ) were placed on 
the soil surface, and the percentage of dispersed particles falling through the 
vegetation canopy into the planchets was determined on a weight per unit area 
basis. This experiment was repeated three times, and the results were averaged. 

Twenty days after fallout dispersal, samples of terminal buds, leaf axils, leaf 
blades, and stems were collected from V. porteri plants in each irradiated 
community. Three surface and three subsurface (0.5-cm) soil samples were also 
collected from each community. To determine the relative radioactivity per unit 
area of plant parts and soil, we pressed all samples flat in planchets for counting. 
Stems and buds were sectioned longitudinally and oriented so that their external 
surfaces faced the detector. 



Community Analysis 

Ecosystem Metabolism 

A Beckman Instruments, Inc., model 215 infrared gas analyzer was used to 
measure rates of net production and respiration, based on the difference 
between concentrations of carbon dioxide (CO2 ) in ambient air and in air 
sampled from the experimental communities. Bourdeau and Woodwell 22 
reviewed infrared absorption techniques for measuring rates of C0 2 exchange. 
Lugo 1 5 measured rates of C0 2 exchange in granite-outcrop communities using 
techniques similar to those presented here. 



460 



MURPHY AND McCORMICK 



The gas-analysis system is shown in Fig. 2. The transparent metabolism 
chamber (Fig. 3) was partitioned through the center so that air could be sampled 
alternately from control and treatment communities. Two fans approximately 
50 cm in diameter, one in each half of the chamber, supplied an airflow 
averaging 34 cm/sec across each community and maintained the internal 




VALVE 



PUMP 



JV- 



FLOWMETER 



DESICCATOR 



NFRARED 
GAS ANALYZER 



Fig. 2 Diagram of the system used to measure rates of CO 2 exchange in the 
experimental outcrop communities. Arrows indicate direction of airflow. 



chamber temperature within ±3°C of outside ambient air. Airflow was measured 
at nine points over the cross section of each half of the chamber with a hot-wire 
anemometer. On the average, the volume of air in each half of the chamber was 
replaced 13 times per minute. Known concentrations of C0 2 in nitrogen were 
used to calibrate the gas analyzer. 

The following relation was used to convert differences between C0 2 
concentrations in ambient air and those in chamber air to rates of ecosystem net 
production or nighttime respiration in grams of carbon per square meter of 
ecosystem per hour (g C/m 2 /hr): 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 461 

''s-A.i 




Fig. 3 Transparent chamber used for measuring rates of ecosystem CO 2 
exchange. The chamber is shown in position over one of the experimental 
outcrop communities. 



gC/m 2 /hr = 



flow rate 



difference 



273 



12 g C/mole 



X 60 min/hr 



(liters/min) in C0 2 (ppm) temp, in K 22.4 liters/mole 
ecosystem area (m 2 ) X 10 6 jid/liter 

Measurements of C0 2 exchange rates were taken over a 4-day period 12 days 
before fallout dispersal and over a 4-day period 43 days after fallout dispersal. 
Each of the four irradiation and control communities was measured for one 
clear, sunny day before and after the irradiation period. Ambient-air and 
chamber-air samples were analyzed at the following times during the day for 
calculation of rates of net production: 9:30 to 10:10 a.m., 12 noon to 
1:10 p.m., and 4:00 to 4:40 p.m. To calculate a reference rate of nighttime 
respiration, we analyzed ambient-air and chamber-air samples between 9:30 and 
10:10 p.m. These rates were considered representative of early nighttime only 
(Lugo 15 found rates of nighttime respiration in outcrop communities to be 
maximum between 9:30 and 10:10 p.m. in June 1968). Each half of the divided 
chamber and the ambient air were sampled for 10 min in a 30-min cycle during 
each of the sampling periods. Ten readings were taken during each 10-min 
period. 



462 MURPHY AND McCORMICK 

Species Composition 

All plants were identified and counted in each of the communities 20 days 
before and 56 days after fallout dispersal. For lichens, mosses, and sedges, 
percent cover rather than numbers of individuals was estimated by using a 
20-cm 2 wire frame as a gauge. 

Bio mass 

One 20- by 40-cm quadrat was harvested from the center of each community 
69 days after fallout dispersal. The plants in each sample (almost exclusively 
V. porteri) were divided into stem (with roots), leaf, and flower-head portions, 
oven dried for 24 hr at 105°C, and weighed. 

Leaf -Area Index 

The ratio of leaf area to ground area was estimated in all communities by 
suspending a weighted string over each intersection of grid lines (15 measure- 
ments per community). The number of leaves (of any plants) touching the 
vertical string was taken as an estimate of leaf-area index, and an average value 
was calculated for each community. This method was developed by Odum. 23 
The estimation was made 4 days before and 49 days after fallout dispersal. 

Canopy Stratification 

To determine the magnitude of the shift in canopy height with plant growth, 
we positioned a graduated aluminum rod perpendicular to the ground at each 
intersection of grid lines (15 per community) and recorded the height of all 
leaves touching the rod. The number of leaves in each increment of height above 
the ground for the 15 positions was calculated. This measurement was taken 
4 days before and 49 days after fallout dispersal in all communities. 

Litter Accumulation 

Four aluminum pans with a total area of 380 cm 2 were placed in each 
experimental community to catch fallen plant debris. The oven-dry (24 hr at 
105°C) weight of accumulated matter was determined 54 and 82 days after 
fallout dispersal. The mean weight per community was converted to a square 
meter basis. 



Analysis of the Summer-Dominant Viguiera porteri 

Height Growth 

The distance from ground level to terminal buds was measured 20 days 
before and 56 days after fallout dispersal in 60% or more of all Viguiera plants in 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



463 



all communities. The measured individuals were selected at random. Growth was 
expressed as percent increase in height during the period between fallout 
dispersal and the measurement 56 days later. 

Terminal Bud Mortality 

The terminal buds of 50 randomly selected Viguiera plants in each 
community were classified 70 days after fallout dispersal as either normal or 
dead, based on whether they showed signs of growth. The number of dead buds 
was expressed as a percentage of the 50 buds observed in each community. 

Pigment Diversity 

To document a possible change in coloration, we determined the yellow-to- 
green-pigment ratio 24 (Margalef ratio) 21 days before and 65 days after fallout 
dispersal. Pigments were extracted from three samples of three leaves each from 
each community. Leaves were ground in 90% acetone to extract pigments. 25 
Optical densities of the samples were measured with a spectrophotometer at two 
wavelengths, 430 and 665 mju. The ratio of the optical density at 430 mji to that 
at 665 mjU was taken as the pigment-diversity ratio. 

RESULTS 



Dosimetry 

Dose levels obtained on the ground and in the vegetation canopy are given in 
Table 1. In the low-dose communities, the mean ground-surface dose (4824 rads) 
was 1.6 times higher than the mean canopy dose (2996 rads). In the high-dose 
communities, the ratio of mean ground-surface dose (8770 rads) to mean canopy 



Table 1 

MEAN COMMUNITY DOSE LEVELS AFTER 3 3 DAYS OF 
EXPOSURE TO FALLOUT SIMULANT* 







Dose, rads 




Treatment 


Soil surface 


Canopy 


Mean 
(canopy and surface) 


Low dose 
Control 

High dose 
Control 


4824 ±882 
1.5 ±0.3 

8770 ±676 
3.0 ±2.0 


2996 ± 326 
2.0 ±0.2 

5092 ±743 
4.5 ± 1.7 


4037 ±768 
1.8 ±0.2 

7082 ± 38 

3.8 ± 1.8 



*Each value (± 1 standard error) represents the mean of two replicate 
communities. 



464 



MURPHY AND McCORMICK 



dose (5092 rads) was 1.7. The mean integrated high dose (mean of ground and 
canopy) was 7082 rads, 1.8 times higher than the mean integrated low dose 
(4037 rads). 

The doses recorded by the glass-vial lithium fluoride dosimeters after their 
27-hr exposure in the high-dose communities are shown in Fig. 4. About a third 
(2000 rads) of the mean integrated dose (7082 rads) was received during the 
initial 27-hr period in the high-dose communities. Ground-surface doses were 1.8 
times higher than canopy doses during the early period. 




1000 



2000 
DOSE, rads 



3000 



Fig. 4 Initial 27-hr doses recorded by the 10 lithium fluoride dosimeters in 
the high-dose communities. 



Experiments with nonradioactive fallout simulant showed that 40% by 
weight of all particles dispersed over the communities was initially retained on 
vegetation. The radioactivity per unit area of plant surfaces relative to that of 
the soil surface 20 days after fallout dispersal is shown in Fig. 5. The surfaces of 
leaf axils and terminal buds apparently collected more radioactive particles than 
did other plant parts, but even these surfaces were only 2 3 and 14%, 
respectively, as radioactive as the soil surface. The surfaces of leaf blades and 
stems were less than 5% as radioactive as the soil surface. At a depth of 0.5 cm, 
there was no radioactivity above background in the soil. 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



465 



00 









— 


80 


- 




- 




- 




- 


60 






- 




— 




- 


40 


- 




- 




— 




1 


— 


20 


1 


1 


— 




' 


i 




' 1 i 


n 


_. _ 1.. _* 1 



SOIL 
SURFACE 



LEAF 
AXILS 



TERMINAL 
BUDS 



LEAF 
BLADES 



STEM SUB- 
SURFACES SURFACE 
SOIL 



Fig. 5 Mean radioactivity of Viguiera porteri plant parts relative to the 
radioactivity of the soil surface. Vertical lines indicate ±1 standard error of the 
mean. 



Response of the Plant Community 



General Appearance 



Beta radiation did not change the overall appearance of the experimental 
communities (Fig. 6). Changes in community structure required close observa- 
tion and measurement for detection. 



Ecosystem Metabolism 

Mean rates of net production for replicated communities between 9:30 a.m. 
and 4:40 p.m. on clear days, before and after irradiation (July and September, 
respectively), varied from 1.0 to 1.4gC/m 2 /hr (Table 2) and averaged 1.2 in 
both months. There was no change in the overall balance of CO2 exchange 
during the daytime between July and September in control or irradiated 
communities when replicate values were averaged. Representative curves of rates 
of net production, based on the three periods of daytime measurement, and 
curves of solar radiation and metabolism-chamber temperatures are shown in 
Fig. 7. 

For the 40-min dark period measured each night (9:30 to 10:10 p.m., the 
period of maximum nighttime respiration rates as shown by Lugo 1 5 ), respiration 



466 



MURPHY AND McCORMICK 




Fig. 6 Experimental outcrop community approximately 6 weeks after ap- 
plication of fallout simulant. The right half of the community received a mean 
dose of 7000 rads, and the left half, shielded by a plexiglass sheet, was a 
control. 

Table 2 

MEAN RATES OF NET PRODUCTION (NP) IN THE EXPERIMENTAL 

COMMUNITIES BETWEEN 9:30 A.M. AND 4:40 P.M. 

IN JULY AND SEPTEMBER* 







July (preirradiation) 


Septem 
Date 


ber 


(postirradiation) 


Treatment 


Date 


NP, g 


C/m 2 /hr 


NP, gC/m 2 /hr 


4000 rads 


17 


18 


1.4 


±0.6 


15, 


16 




1.4 ±0.4 


Control 


17 


18 


1.2 


±0.3 


15, 


16 




1.2 ±0.1 


7000 rads 


16 


19 


1.0 


±0.1 


13, 


14 




1.1 ±0.2 


Control 


16 


19 


1.0 


±0.3 


13, 


14 




1.0 ±0.1 



*Each value (±1 standard error) is based on 80 readings of CO2 exchange 
rates and represents the mean of two replicate communities. 



rates for replicated communities varied from 1.7 to 3.6gC/m 2 /hr (mean, 2.9) 
before irradiation in July and from 1.2 to 4.0gC/m 2 /hr (mean, 2.2) after 
irradiation in September (Table 3). In six of the eight communities, the rate of 
respiration declined between July and September. In two communities 
(7000 rad and 7000-rad control), the rate increased. 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



467 




9 a.m. 10 



12 1p.m. 2 

TIME 

(b) 



Fig. 7 Representative curves of solar radiation, chamber-air temperature, and 
rates of net production in the experimental outcrop communities 43 days 
after fallout dispersal, (a) 4000-rad community on September 16. (b) 7000-rad 
community on September 14. — , net production rates for irradiated com- 
munities; — , net production rates for control communities; I, ± 1 standard 
error of the mean. 



468 MURPHY AND McCORMICK 

Species Composition 

The summer flora of the simulated outcrop communities consisted of the 
following species: Viguiera porteri (A. Gray) Blake (Asteraceae), Senecio 
tomentosus Michx. (Asteraceae), Talinum teretifolium Pursh. (Portulacaceae), 
Crotonopsis elliptica Willd. (Euphorbiaceae), Hypericum gentianoides (L.) BSP. 
(Hypericaceae), Bulbostylis capillaris (L.) Clarke (Cyperaceae), Polytrichum 
commune Hedvv. (Polytrichaceae), and Cladonia sp. (Cladoniaceae). 



Table 3 

MEAN RATES OF RESPIRATION (R) IN THE EXPERIMENTAL 
COMMUNITIES BETWEEN 9:30 AND 10:10 P.M. IN JULY AND SEPTEMBER* 





July (preirradiation) 


September 
Date 


(postirradiation) 


Treatment 


Date 


R, gC/m 2 /hr 


R, gC/m 2 /hr 


4000 rads 
Control 

7000 rads 
Control 


17, 18 
17, 18 

16, 19 
16, 19 


3.6 ±0.2 

1.7 ±0.5 

2.7 ±0.9 
3.6 ±1.6 


15, 16 
15, 16 

13, 14 
13, 14 


1.6 ±1.1 

1.2 ±0.8 

1.8 ±1.4 
4.0 ±0.1 



*Each value (±1 standard error) is based on 20 readings of C0 2 exchange 
rates and represents the mean of two replicate communities. 



In only one species, B. capillaris, was there a reduction in quantity (percent 
cover) which appeared related to radiation. The percent cover of this sedge 
increased by an average of 12% in control and 4000-rad communities but 
decreased by 17% in the 7000-rad communities. 

Bio mass 

Nearly 100% of all plants in the biomass samples were V. porteri. Total 
biomass was unrelated to the number of plants in the harvested quadrats 
(Table 4). Of the four irradiated communities and their controls, total biomass 
was least in the 7000-rad communities (585 g/m 2 , or 16% less than in the 
7000-rad control communities). The reduction was due to a lower production of 
flower and stem biomass. Leaf biomass was similar to control levels in all 
irradiated communities. 

The community treated with nonradioactive fallout simulant and its control 
had 250 and 200 g/m 2 total biomass, respectively, or about 64% less than the 
other communities (Table 4). These communities were transplanted 1 year later 
than the others and were more sparse in appearance. Nonradioactive fallout 
simulant did not reduce biomass production. 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



469 



Table 4 
BIOMASS OF Viguiera porteri IN OCTOBER, 69 DAYS AFTER FALLOUT DISPERSAL* 





Mean 
number 




2 
Dry weight, g/m 














Treatment 


of plants 


Stems 


Leaves 


Flower heads 


Total 


4000 rads 


16 


485 ±25 


118 ± 12 


82 ±5 


681 ± 32 


Control 


28 


460 ± 86 


99 ± 14 


72 ±5 


631 ± 106 


7000 rads 


13 


425 ±60 


112 ±20 


55 ±12 


585 ±35 


Control 


24 


496 ± 35 


105 ±19 


92 ±2 


693 ±19 


Nonradioactive 












falloutt 


20 


166 


45 


38 


250 


Controlt 


33 


125 


46 


30 


199 



*Each value (±1 standard error) represents the mean of two replicate communities 
unless otherwise indicated. 

tEach value represents one community. 



Table 5 

MEAN LEAF-AREA INDEX AND PERCENT INCREASE 
BETWEEN JULY AND SEPTEMBER* 





July 


September 


Percent 


Treatment 


(preirradiation) 


(postirradiation) 


increase 


4000 rads 


2.4±0.3 


3.2 ±0.2 


34 ± 8.6 


Control 


2.2 ±0.2 


3.2 ±0.4 


53 ±31.5 


7000 rads 


1.6 ±0.2 


1.9 ±0.2 


19 ± 2.0 


Control 


1.6 ±0.1 


2.5 ±0.5 


54 ±21 .5 


Nonradioactive 








falloutt 


1.1 


1.3 


18 


Controlt 


0.8 


0.9 


12 



*Each value (±1 standard error) represents the mean of two replicate 
communities unless otherwise indicated. 
tEach value represents one community. 



Leaf -Area Index 

Mean leaf -area index varied from 1.6 to 3.2 in the irradiated communities 
and in their controls and was variable (Table 5). The 7000-rad communities 
showed a smaller increase in leaf-area index (19%) than controls (54%) for the 
49-day period after fallout dispersal. The final leaf-area index in the 7000-rad 
communities (1.9) was 24% lower than that in the control communities (2.5). 



470 



MURPHY AND McCORMICK 



The final leaf-area index in the 4000-rad communities and in their controls was 
the same (3.2). The index increased 6% more in the community treated with 
nonradioactive fallout simulant than in the control. 

Can opy S tra tifica tio n 

The increase in height of the plant canopy (almost 100% V. porteri) during 
the growing season between July and September is obvious in all communities in 
Fig. 8. In the 7000-rad communities, there was a maximum concentration of 
leaves 50 cm above the ground in September, whereas in the controls the leaves 
were more uniformly distributed between about 40 and 70 cm in height. The 
vertical distribution of leaves in the 4000-rad communities was similar to that in 
the controls. All irradiated and control communities showed a decrease in the 
number of lower leaves with increase in plant height, a natural phenomenon. 



JULY 



SEPTEMBER 




- 


1 1 


i 


Jk 


1 


_ 




//\\f 


\\ 


d 




A i 






J \ 




i 


1 




1 *• 



40 80 




(b) 
HEIGHT ABOVE GROUND, cm 




Fig. 8 Canopy stratification in the experimental outcrop communities. The 
total number of leaves at various heights in the canopy is shown for the 15 
measured locations in each irradiated and control community, (a) 4000-rad 

communities, (b) 7000-rad communities. — , irradiated communities; , 

control communities. 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 471 

Litter Accumulation 

During the 56-day period between July 29 and September 2 3, the daily litter 
accumulation was 3 3% greater in the 7000-rad communities than in the controls 
(Table 6). In the 4000-rad communities, the daily accumulation was 20% less 
than in the controls. During the 28-day period between September 23 and 
October 21, the daily accumulation was 44% greater in the 7000-rad com- 
munities than in the controls. In the 4000-rad communities, the daily 
accumulation was 18% less than in the controls. 



Table 6 

MEAN DAILY LITTER ACCUMULATION DURING TWO 
CONSECUTIVE PERIODS FOLLOWING FALLOUT DISPERSAL' 

2 
Accumulation, g/m /day 



Treatment July 29 to Sept. 23 Sept. 23 to Oct. 21 

4000 rads 0.4 ±0.1 3.6 ±0.1 

Control 0.5 ±0.2 4.4 ±0.1 

7000 rads 0.4 ±0.1 4.9 ±0.8 

Control 0.3 ±0.1 3.4 ±0.4 

*Each value (±1 standard error) represents the mean of two 
replicate communities. 



Response of the Summer-Dominant Viguiera porteri 

Height Growth 

Percent increase in height in V. porteri, adjusted for the 56-day period from 
August 1 (the day after fallout dispersal) to September 26, is given in Table 7. 
The mean percent height increase in the 7000-rad communities (55%) was 37% 
less than in the controls (92%). Growth may have been slightly reduced in the 
4000-rad communities, but the standard errors of the means indicated that there 
was considerable overlap of growth values between irradiated and control 
communities. Increase in height in the community treated with nonradioactive 
fallout simulant was 91% and in the control 93%. 

Terminal Bud Mortality 

Beta radiation killed 46% of the terminal buds in the 7000-rad communities 
and 16% in the 4000-rad communities (Table 7). The frequency of dead terminal 
buds ranged from 2 to 4% in control communities. The stunted appearance of a 
V. porteri plant with a dead terminal bud and the compensatory development of 



472 MURPHY AND McCORMICK 



Table 7 



MEAN PERCENT HEIGHT INCREASE DURING THE 56-DAY PERIOD 

FOLLOWING FALLOUT DISPERSAL AND PERCENT TERMINAL-BUD 

MORTALITY IN Viguiera porteri* 





Height 


Terminal- 


Treatment 


increase, % 


bud mortality, % 


4000 rads 


87 ±4 


18 ±2 


Control 


92 ±4 


2±2 


7000 rads 


55±4 


49 ± 3 


Control 


92 ±5 


3±1 


Nonradioactive 






falloutt 


91 


4 


Controlt 


93 


4 



*Each value (±1 standard error) represents the mean of two replicate 
communities unless otherwise indicated. 
tEach value represents one community. 

lateral branches can be seen in Fig. 9. Nonradioactive fallout simulant did not 
affect terminal-bud development, but there was 4% mortality in both treated 
and control communities. 

Pigment Diversity 

The yellow-to-green-pigment ratio was higher (mean, 5.2) toward the end of 
the growing season in October than in July (mean, 2.8) in all communities 
(Table 8). The optical density of pigment samples at both 430 and 665 m/d 
declined toward late summer, but the optical density at 665 mfi declined most, 
accounting for the increased ratio. There was no change in this ratio associated 
with irradiation. The ratio in the community treated with nonradioactive fallout 
simulant increased 2 3% more than that in its associated control community. 

DISCUSSION 
Fallout-Radiation Field 

The radiation field from fallout simulant was vertically stratified in all 
communities. Doses on the ground surface exceeded those in the vegetation 
canopy 40 cm above the ground by 65%. Approximately a third of the 
integrated dose was delivered within the first 27 hr after fallout dispersal, during 
which time a maximum of 40 wt.% of the particles still resided on the 
vegetation. During the remainder of the exposure period, all visible particles 
were on the soil surface owing to a heavy ram 24 hr after fallout dispersal. No 
radioactive particles were detected 0.5 cm beneath the soil surface. 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 



473 




Fig. 9 Viguiera porteri plant with dead terminal bud. The ruler is 15 cm long. 



The mean integrated beta-bath and contact dose levels recorded by the 
dosimeters cannot be directly related to all the observed biological effects. 
Certain plant parts, such as leaf axils and terminal buds, captured and retained 
fallout particles and doubtlessly received higher than average doses. The 
maximum doses recorded by some dosimeters may be better estimates of the 
contact dose received by terminal buds that were killed. Twenty-two percent of 
the dosimeters in the low-dose communities (mean dose, 4000 rads) gave values 
between 7000 and 10,000 rads, and 18% of the dosimeters in the high-dose 
communities (mean dose, 7000 rads) gave values between 11,000 and 
13,000 rads. The dosimeters recording maximum doses were visibly coated with 
fallout simulant while the activity of the 90 Y was still high. These dose values 
may therefore approximate the actual doses received by some plant parts that 
trapped fallout simulant. 

The data showed no negative biological response to nonradioactive fallout 
simulant applied at the same density (111 g/m 2 ) as the radioactive simulant. A 



474 



MURPHY AND McCORMICK 



Table 8 

MEAN MARGALEF PIGMENT-DIVERSITY RATIOS IN 
Viguiera porteri IN JULY AND SEPTEMBER* 





Pigment-diversity ratio 




July 


September 


Treatment 


(preirradiation) 


(postirradiation) 


4000 rads 


2.86 ±0.06 


5.11 ±0.21 


Control 


2.80 ±0.06 


5.00 ±0.16 


7000 rads 


2.75 ±0.02 


5.18 ±0.14 


Control 


2.76 ±0.04 


5.36 ±0.48 


Nonradioactive 






falloutt 


2.72 


5.81 


Controlt 


2.87 


4.78 



*Eaeh value (±1 standard error) represents the mean of 
two replicate communities unless otherwise indicated. 
tEach value represents one community. 



pilot study (unpublished data) showed no changes in rates of C0 2 exchange of 
several species of small herbs treated with 111 g/m 2 and higher densities of 
nonradioactive fallout simulant. It was interpreted that the effects observed in 
this study were due to beta radiation and not the fallout particles themselves. 

Questions relating to four of the objectives of this study can now be 
considered: (1) What were the effects on the overall integrated functioning, or 
metabolism, of the system? (2) What were the effects on the community 
structure, and how did these effects relate to the overall metabolism? (3) How 
did the severity of beta effects compare with that of gamma in earlier studies? 

Ecosystem Metabolism 

Odum 2 6 defined stress as the drain of calories of potential energy flow and 
noted that the change in energy flow in a stressed system can be used as a 
measure of the stress. "The stress of a disordering, damaging radiation," he 
pointed out, "resembles an increase in temperature by increasing the rate of 
random deformations of microscopic structures necessary to regular work and 
maintenance processes." Energy is thus diverted from the production of biomass 
to maintenance processes; therefore rates of net photosynthesis would be 
expected to decrease and rates of respiration to increase. 

A measure of energy flow in ecosystems is metabolism, as measured by 
determining rates of C0 2 exchange. The C0 2 exchange data showed no sign of 
beta-radiation stress when the outcrop communities were measured 43 days after 
fallout dispersal. The rates of net production in grams of carbon per square 
meter per hour obtained in this study (mean daytime rate, 1.2 in both July and 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 475 

September) agree closely with measurements by Lugo 1 5 in very similar 
simulated outcrop plant communities during the previous summer (mean, 1.3). 
According to most measurements in this study, maximum rates of net 
production occurred in the morning, during which time the concentration of 
CO2 in the air around the communities was still high (27% higher at 9:30 a.m. 
than at 12 noon), temperatures were relatively low (32% lower at 9:30 a.m. than 
at 12 noon), soil-moisture conditions were most favorable, concentrations of 
nutrients in the soil from the previous night's respiration were still high, and 
photorespiration effects were low. Morning rates of net production were also 
found to be maximum by Lugo. 1 

Rates of nighttime respiration during the 40-min measurement period from 
9:30 to 10:10 p.m. declined from a mean of 2.9gC/m 2 /hr in July to 2.2 in 
September. This decline was likely caused by the facts that the nighttime 
ambient-air temperature was about 9°C cooler in September and the daily 
accumulation of labile organic matter was less because of lower light intensities. 
There was a slight increase in rates of nighttime respiration in one control and 
one irradiated community. 

Measured rates of nighttime respiration were higher than mean rates of net 
production, but the respiratory rates were representative of only a short period 
during the early part of the night. Lugo 1 5 reported rates of respiration averaging 
6.1 gC/m 2 /hr during the same period of the night in similar communities in 
June, but he found the average rate for the entire night to be much lower 
(1.6 g C/m 2 /hr). These initial high rates, which occur while storages of organic 
matter produced during the preceding daytime period are maximum, demon- 
strate the importance of restricting comparisons to values obtained during 
equivalent time periods. 

Carbon dioxide exchange has been used before to measure metabolic effects 
of ionizing radiation stress. Hadley and Woodwell 2 7 showed that acute exposure 
to as little as 1250 R of gamma radiation depressed rates of net photosynthesis 
in pine leaves without affecting rates of C0 2 evolution in the dark. In pine stems 
rates of C0 2 evolution were initially stimulated but ultimately depressed. 
Woodwell 28 found that irradiation at 3 3 R/day (total dose unspecified) 
depressed both rates of C0 2 fixation and respiration in a forest ecosystem, net 
photosynthesis being depressed more than respiration. 

The extent to which metabolic data can be expected to reflect stress-induced 
changes in the energy flow of an ecosystem depends on the system and the time 
of measurement. Natural ecosystems are capable of repair, through succession, 
but the ease with which the system is disrupted and the rates of repair which 
follow can be expected to vary depending on the nature of the biological 
components of that system and the extent of damage done. Systems composed 
of small units depend more on replacement to maintain themselves than do 
systems composed of large units. 26 A forest would take longer for repair than an 
actively growing algal culture, and the measurable metabolic effects in the forest 
would presumably be evident for a longer time after the stress was removed. This 



476 MURPHY AND McCORMICK 

is not to say that the algal culture would not be more vulnerable to extinction 
than the complex forest system. 

The situation in the outcrop communities is similar to that in an old field, 
and, as Woodwell 28 pointed out, species diversity appears to be a more sensitive 
indicator of radiation response than organic production, although the signifi- 
cance of this response is incompletely understood. Radiosensitive species in an 
old field are eliminated by radiation, but they are replaced by species that are 
radioresistant, bringing about changes in the relative importance of plant 
populations without necessarily causing changes in total biomass. That the ratio 
of primary production to biomass is increased in the less diverse system is an 
indication of successional setback in systems with initial low diversity. 3 ' 29 
Radiation-induced reduction in species diversity has been observed in outcrop 
communities. Garrett 30 found a decline in diversity associated with gamma 
irradiation, and McCormick and Piatt 1 8 noted the expansion of the sedge 
Bulbostylis capillaris into the zone that had been occupied by Viguiera porteri in 
an outcrop community that received more than 30,000 R of gamma radiation. 

Community Structural Response 

Only one plant species exhibited immediate mortality in the experimental 
outcrop communities. The percent cover of Bulbostylis capillaris declined by 
17% in the 7000-rad communities, whereas it increased by an average of 12% in 
the other communities. Gamma-radiation studies indicated that this species is 
radioresistant, 1 8 but, since B. capillaris (a sedge) has growing apexes close to the 
ground, it may have retained high densities of fallout particles in close proximity 
to sensitive meristems. The geometry of the fallout radiation field was such that 
the physical position of plants within the community was at least as important 
as their inherent degree of tolerance to radiation. 

High levels of radioactivity on or near the soil surface (65% higher than at 
40 cm above the ground) represent an important aspect of the radiation field. In 
the gamma-field studies, which provided the basis for predictions of effects of 
thermonuclear war on ecosystems, soil organisms, roots, seed, and plant 
meristems near the soil surface were afforded some protection by microrelief 
and litter. In fallout situations the soil component of the ecosystem, recognized 
as being an important pathway of energy flow, is more vulnerable, and the 
effects occurring in and near this component of the system warrant much closer 
study. 

Viguiera porteri plants in the 7000-rad communities grew 37% less in height 
than did control plants over the 56-day period after fallout dispersal. The mean 
beta-bath dose received by the terminal portions of these plants was about 
5000 rads. The total dose, including contact dose due to entrapped particles, is 
not known but is assumed to be higher, possibly approximated by the highest 
dosimeter doses (11,000 to 13,000 rads). McCormick and Piatt 18 found a 17% 
reduction in height growth in V. porteri plants that had accumulated a total dose 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 477 

of 5000 R from gamma radiation ( 60 Co) over a 100-day period. A reduction 
equivalent to the 37% observed in this study required about 17,000 R. If the 
beta dose level responsible for the 37% reduction observed was assumed to be 
5000 rads, the RBE for acute exposure to beta radiation relative to chronic 
exposure to gamma radiation would be about 3.4. If the dose levels responsible 
were considered to be near the maximum observed (11,000 to 13,000 rads), the 
RBE would be about 1.3. The actual RBE is probably near 2 for height-growth 
reduction in V. porteri under the conditions outlined. 

The morphological explanation for the beta-radiation-induced height-growth 
reduction is quite clear. In the communities that received a canopy dose of 
5000 rads, 18% of all V. porteri terminal buds were killed. Terminal buds were 
especially vulnerable to fallout irradiation since they were actively growing and 
retained more radioactivity per unit area than did other plant parts except for 
leaf axils. 

The total biomass (V. porteri accounted for almost 100% of the harvested 
biomass) was 16% less in the 7000-rad communities than in the controls. The 
retarded height growth was most likely the mam contributor to this reduction in 
biomass. Interestingly, however, there was no reduction in leaf biomass in any of 
the irradiated communities. The accelerated growth of lateral branches helped to 
provide a normal leaf biomass. Woodwell 8 noted an actual increase in total 
standing crop in an old field at exposures of up to 1000 R/day, but higher 
exposures caused a sharp decline in standing crop. In this study flower biomass 
was reduced by 40% in the 7000-rad communities. Reproduction is an 
energetically expensive process owing to the expenditure necessary to produce 
and organize complex structures (including complex molecules such as DNA) 
and the high caloric content of reproductive structures. 3 x Possibly some of the 
energy that would normally have been used in this process was instead diverted 
to the observed repair mechanisms (primarily lateral branch development). 
Normal rates of basal metabolism could not have been expected to supply the 
stress-induced demand for maintenance energy. 

The final (September) leaf-area index was the same (3.2) in the 4000-rad 
communities and in their controls. The final leaf-area index in the 7000-rad 
communities was 1.9, 24% lower than in the controls. The fact that leaf-area 
index was reduced even though biomass of leaves was not can be explained by 
the orientation of leaves on the terminal shoots of the canopy plants (V. 
porteri). In plants with dead terminal buds, the leaves on the central shoot 
developed, but they were clustered together around the shoot apex because of 
the lack of internodal elongation. Clustered leaves resulted in an underestimation 
of leaf-area index as measured with the weighted-string method. The data on 
canopy stratification indicated that there was no essential difference between 
the vertical distribution of leaves in the 4000-rad communities and the controls. 
In the 7000-rad communities, however, there was a maximum concentration of 
leaves at 50 cm above the ground. This reflected the stunted nature of the 



478 MURPHY AND McCORMICK 

dominant V. porteri and contrasted with a more continuous vertical distribution 
of leaves at about 40 to 70 cm in the controls. 

These differences in canopy structure in the 7000-rad communities, a lower 
leaf-area index and a more clustered vertical distribution of leaves, were results 
of terminal-bud mortality and the subsequent compensation by lower lateral 
branches after the reduction in terminal growth. The differences were not caused 
by radiation-induced leaf fall. Litter accumulation data gave no evidence of 
unusually fast rates of leaf fall until after the second leaf-area-index measure- 
ment had been taken. After that period, in October, the rate of daily litter 
accumulation was 43% more rapid in the 7000-rad communities than it was in 
the controls. 

Pigment Diversity 

Color changes in plants, especially in leaves, are a common effect of ionizing 
radiation. The visual indexes of discoloration sometimes used to document 
these changes seem inadequate. They are subjective and tell nothing about the 
cause of discoloration. The Margalef pigment-diversity ratio seems to be of value 
in this regard since leaf yellowing should be indicated by an increased 
yellow-to-green-pigment ratio. As the V. po rf m'-dominated outcrop communi- 
ties progressed into senescence during the postirradiation period in September, 
they all appeared more yellow, and the pigment-diversity ratio increased from a 
mean of 2.8 in July to 5.2 in September. The increase was caused by a greater 
decline in green-pigment concentration than in yellow. The communities stressed 
with fallout, however, showed no excessive discoloration visually, and the 
pigment-diversity ratio in V. porteri gave no indication of any unusual yellowing 
relative to controls. 

Homeostasis in the Outcrop Plant Community 

The granite-outcrop plant community possesses plasticity, the intrinsic 
capacity for rapid repair relative to larger terrestrial systems. The community is 
able to quickly fill gaps in utilization of its resources because of the short life 
cycles of its component species, the array of life forms of these species, 13 the 
specialized mechanisms of seed germination, 33 and the high rates of primary 
production under favorable conditions. 15 Not only is the herbaceous com- 
munity able to replace eliminated components quickly but also the damaged 
components are in themselves capable of rapid compensation in structure for 
damaged parts. If new individuals do not actually fill the gaps, the remaining 
viable individuals will. 

Harper 34 pointed out that the plasticity shown by most plants makes sheer 
numbers a misleading measure of the actual amount of a species present. 
Plasticity in the outcrop community is illustrated by the fact that the biomass of 
V. porteri per unit area was unrelated to the number of plants per unit area. Ten 
plants in one area, in fact, produced more biomass (620 g/m 2 ) than 48 plants in 



ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 479 

a comparable area (525 g/m 2 ). Under normal environmental conditions an 
outcrop community is adapted to production of a particular organic matter and 
is stabilized against changes in that value through feedback mechanisms related 
to light, nutrient, and water supply. Removal of competing plants from within a 
population or from a different population, which relieves the demand on water 
and nutrient resources and allows the penetration of more light into the canopy, 
would help to explain the lack of relation between number of individuals and 
biomass. One of the consequences of a density stress on a plant population is a 
plastic response from the individuals as they adjust to share limiting resources. 35 

The best example of an adjustment in outcrop-plant morphology to 
beta-radiation damage which helped maintain metabolic and structural homeo- 
stasis in the community was the development of lateral branches in V. porteri 
when the terminal buds were killed. Skoog 36 attributed this common radiation 
effect to the destruction of auxin in terminal buds; this then releases lateral buds 
from apical dominance. Even when there was severe damage to individual plants, 
the general appearance and structure of the experimental communities were not 
greatly changed by beta radiation, owing primarily to lateral branch development. 

This capacity for rapid adjustment may be partially explained by the fact 
that elements of the prevailing environmental conditions under which the 
outcrop ecosystem evolved are in themselves stresses. Woodwell 28 suggested that 
plants capable of adjusting to environmental stresses are better able to cope with 
radiation stress. Outcrop plants possess such mechanisms. Periods of low rainfall 
and high temperatures are not' unusual during the summer growing season. 15 
The ability to recover from extreme wilting has been shown in V. porteri. " 
Lugo 1 5 found that, under optimal conditions of temperature, light intensity, 
and moisture, outcrop communities are capable of much higher than average 
rates of net production. During unfavorable periods the rates of C0 2 exchange 
are much reduced; this conserves energy reserves. 

In 1963 Margalef 3 7 predicted the destruction of structure in ecosystems by 
ionizing radiation without any great change in energy flow. The primary reason 
for our not finding a change in rates of C0 2 exchange correlated with radiation 
damage in this investigation is that the community had compensated structurally 
by the time the measurements were taken. Physical signs of radiation damage in 
plants were visible at the time C0 2 exchange was measured, but the 
morphological adjustments made by these plants, primarily lateral branch 
development, compensated to the point where the system was able to maintain 
normal levels of energy accumulation and utilization. 

ACKNOWLEDGMENTS 

This research was sponsored by the U. S. Atomic Energy Commission under 
Contract AT-(40-l)-3 299. Valuable advice was received from H. T. Odum and 
N. Underwood, faculty members of the University of North Carolina, W. B. 
Lane of Stanford Research Institute supplied the fallout simulant and advised in 



480 MURPHY AND McCORMICK 

matters regarding its dispersal, and J. Mackin, also of SRI, calibrated the 
dosimeters. 



REFERENCES 

l.J. F. McCormick, Ecological Analysis of Selected Granite Outcrop Communities and 
Their Response to Chronic Gamma Radiation, M.S. Thesis, Emory University, 1959. 

2. G. M. Woodwell, Effects of Ionizing Radiation on Terrestrial Ecosystems, Science, 138: 
572-577 (1962). 

3. R. B. Piatt, Ionizing Radiation and Homeostasis of Ecosystems, in Ecological Effects of 
Nuclear War, G. M. Woodwell (Ed.), USAEC Report BNL-917, pp. 39-60, Brookhaven 
National Laboratory, August 1965. 

4. E. P. Odum, Summary, in Ecological Effects of Nuclear War, G. M. Woodwell (Ed.), 
USAEC Report BNL-917, pp. 69-72, Brookhaven National Laboratory, August 1965. 

5. G. M. Woodwell, Radioactivity and Fallout: The Model Pollution, Bioscience, 19: 
884-887 (1969). 

6. G. M. Woodwell, Effects of Pollution on the Structure and Physiology of Ecosystems, 
Science, 168: 429-433 (1970). 

7. W. A. Rhoads, R. B. Piatt, and R. A. Harvey, Radiosensitivity of Certain Perennial Shrub 
Species Based on a Study of the Nuclear Excavation Experiment, Palanquin, with Other 
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ECOLOGICAL EFFECTS OF ACUTE BETA IRRADIATION 481 

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EFFECT OF NUCLEAR WAR 

ON THE STRUCTURE AND FUNCTION 

OF NATURAL COMMUNITIES: AN APPRAISAL 

BASED ON EXPERIMENTS 

WITH GAMMA RADIATION 

G. M. WOODWELL and B. R. HOLT 

Biology Department, Brookhaven National Laboratory, Upton, New York 

ABSTRACT 

The combined effects of blast, fallout, fire, and other disturbances that might be associated 
with a nuclear war would involve a complex pattern of changes in natural communities 
which are best described as "loss of structure." The changes include a shift in the 
composition of the communities away from highly integrated arrays of species characteristic 
of evolutionary and successionally mature communities toward the generalists of the 
loosely integrated communities of disturbed areas. This series of changes is accompanied by 
a reduction in net production and frequently by a reduction in the potential of the site to 
support living systems. The changes, which are associated with a wide range of disturbances, 
are especially significant in the case of nuclear war because effects might occur over such 
large areas as to delay the normal processes of recovery. 

Several years ago the Ecological Society of America sponsored a small 
symposium, the proceedings of which were published under the somewhat 
pretentious title "Ecological Effects of Nuclear War." 1 We are asked what can be 
said now, some 7 "nuclear- war less" years later, which was not said then about 
effects on natural communities and their significance for agriculture. The broad 
pattern that we recognized several years ago has not changed at all, but details 
have been added. We understand better now that the effects follow a general 
pattern of wide applicability, which gives a certain limited capacity for 
prediction. 

The quintessence of the pattern was reported faithfully some years ago by 
Punch with specific reference to work at Brookhaven. Punch observed that, if 
you asked the man in the street what radiation would do to a forest, he would 
probably reply that it would kill the trees; Brookhaven scientists had confirmed 
this. The important observation from these studies is almost intuitive to the man 
in the street but is less obvious to scientists: Radiation r